I confirm that point 4) was successful and engine vm was able to autostart, after changing cluster type.

I'm also able to connect to its console from web admin gui

The command line generated now is:

qemu     29450     1 43 23:38 ?        00:03:09 /usr/libexec/qemu-kvm -name guest=HostedEngine,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-10-HostedEngine/master-key.aes -machine pc-q35-rhel8.1.0,accel=kvm,usb=off,dump-guest-core=off -cpu Cascadelake-Server,hle=off,rtm=off,arch-capabilities=on -m size=16777216k,slots=16,maxmem=67108864k -overcommit mem-lock=off -smp 2,maxcpus=32,sockets=16,cores=2,threads=1 -object iothread,id=iothread1 -numa node,nodeid=0,cpus=0-31,mem=16384 -uuid b572d924-b278-41c7-a9da-52c4f590aac1 -smbios type=1,manufacturer=oVirt,product=RHEL,version=8-1.1911.0.9.el8,serial=d584e962-5461-4fa5-affa-db413e17590c,uuid=b572d924-b278-41c7-a9da-52c4f590aac1,family=oVirt -no-user-config -nodefaults -device sga -chardev socket,id=charmonitor,fd=40,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=2020-05-28T21:38:21,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-reboot -global ICH9-LPC.disable_s3=1 -global ICH9-LPC.disable_s4=1 -boot strict=on -device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 -device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 -device pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 -device pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 -device pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 -device pcie-root-port,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 -device pcie-root-port,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 -device pcie-root-port,port=0x17,chassis=8,id=pci.8,bus=pcie.0,addr=0x2.0x7 -device pcie-root-port,port=0x18,chassis=9,id=pci.9,bus=pcie.0,multifunction=on,addr=0x3 -device pcie-root-port,port=0x19,chassis=10,id=pci.10,bus=pcie.0,addr=0x3.0x1 -device pcie-root-port,port=0x1a,chassis=11,id=pci.11,bus=pcie.0,addr=0x3.0x2 -device pcie-root-port,port=0x1b,chassis=12,id=pci.12,bus=pcie.0,addr=0x3.0x3 -device pcie-root-port,port=0x1c,chassis=13,id=pci.13,bus=pcie.0,addr=0x3.0x4 -device pcie-root-port,port=0x1d,chassis=14,id=pci.14,bus=pcie.0,addr=0x3.0x5 -device pcie-root-port,port=0x1e,chassis=15,id=pci.15,bus=pcie.0,addr=0x3.0x6 -device pcie-root-port,port=0x1f,chassis=16,id=pci.16,bus=pcie.0,addr=0x3.0x7 -device pcie-root-port,port=0x20,chassis=17,id=pci.17,bus=pcie.0,addr=0x4 -device pcie-pci-bridge,id=pci.18,bus=pci.1,addr=0x0 -device qemu-xhci,p2=8,p3=8,id=ua-b630a65c-8156-4542-b8e8-98b4d2c48f67,bus=pci.4,addr=0x0 -device virtio-scsi-pci,iothread=iothread1,id=ua-b7696ce2-fd8c-4856-8c38-197fc520271b,bus=pci.5,addr=0x0 -device virtio-serial-pci,id=ua-608f9599-30b2-4ee6-a0d3-d5fb588583ad,max_ports=16,bus=pci.3,addr=0x0 -drive if=none,id=drive-ua-fa671f6c-dc42-4c59-a66d-ccfa3d5d422b,readonly=on -device ide-cd,bus=ide.2,drive=drive-ua-fa671f6c-dc42-4c59-a66d-ccfa3d5d422b,id=ua-fa671f6c-dc42-4c59-a66d-ccfa3d5d422b,werror=report,rerror=report -drive file=/var/run/vdsm/storage/3df8f6d4-d572-4d2b-9ab2-8abc456a396f/df02bff9-2c4b-4e14-a0a3-591a84ccaed9/bf435645-2999-4fb2-8d0e-5becab5cf389,format=raw,if=none,id=drive-ua-df02bff9-2c4b-4e14-a0a3-591a84ccaed9,cache=none,aio=threads -device virtio-blk-pci,iothread=iothread1,scsi=off,bus=pci.6,addr=0x0,drive=drive-ua-df02bff9-2c4b-4e14-a0a3-591a84ccaed9,id=ua-df02bff9-2c4b-4e14-a0a3-591a84ccaed9,bootindex=1,write-cache=on,serial=df02bff9-2c4b-4e14-a0a3-591a84ccaed9,werror=stop,rerror=stop -netdev tap,fds=43:44,id=hostua-b29ca99f-a53e-4de7-8655-b65ef4ba5dc4,vhost=on,vhostfds=45:46 -device virtio-net-pci,mq=on,vectors=6,host_mtu=1500,netdev=hostua-b29ca99f-a53e-4de7-8655-b65ef4ba5dc4,id=ua-b29ca99f-a53e-4de7-8655-b65ef4ba5dc4,mac=00:16:3e:0a:96:80,bus=pci.2,addr=0x0 -chardev socket,id=charserial0,fd=47,server,nowait -device isa-serial,chardev=charserial0,id=serial0 -chardev socket,id=charchannel0,fd=48,server,nowait -device virtserialport,bus=ua-608f9599-30b2-4ee6-a0d3-d5fb588583ad.0,nr=1,chardev=charchannel0,id=channel0,name=ovirt-guest-agent.0 -chardev socket,id=charchannel1,fd=49,server,nowait -device virtserialport,bus=ua-608f9599-30b2-4ee6-a0d3-d5fb588583ad.0,nr=2,chardev=charchannel1,id=channel1,name=org.qemu.guest_agent.0 -chardev spicevmc,id=charchannel2,name=vdagent -device virtserialport,bus=ua-608f9599-30b2-4ee6-a0d3-d5fb588583ad.0,nr=3,chardev=charchannel2,id=channel2,name=com.redhat.spice.0 -chardev socket,id=charchannel3,fd=50,server,nowait -device virtserialport,bus=ua-608f9599-30b2-4ee6-a0d3-d5fb588583ad.0,nr=4,chardev=charchannel3,id=channel3,name=org.ovirt.hosted-engine-setup.0 -device usb-tablet,id=input0,bus=ua-b630a65c-8156-4542-b8e8-98b4d2c48f67.0,port=1 -vnc 172.19.0.224:3,password -k en-us -spice port=5904,tls-port=5905,addr=172.19.0.224,x509-dir=/etc/pki/vdsm/libvirt-spice,tls-channel=main,tls-channel=display,tls-channel=inputs,tls-channel=cursor,tls-channel=playback,tls-channel=record,tls-channel=smartcard,tls-channel=usbredir,seamless-migration=on -device qxl-vga,id=ua-ac7aed4d-d824-40f9-aaa8-1c0be702e38c,ram_size=67108864,vram_size=33554432,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pcie.0,addr=0x1 -device intel-hda,id=ua-c7078e28-5585-4866-bdbd-528ebddd8854,bus=pci.18,addr=0x1 -device hda-duplex,id=ua-c7078e28-5585-4866-bdbd-528ebddd8854-codec0,bus=ua-c7078e28-5585-4866-bdbd-528ebddd8854.0,cad=0 -device virtio-balloon-pci,id=ua-fc4f6b20-0b17-4198-b059-b5753893584d,bus=pci.7,addr=0x0 -object rng-random,id=objua-c4c3e5e7-1c19-4582-a87c-4f3fee4a0ee5,filename=/dev/urandom -device virtio-rng-pci,rng=objua-c4c3e5e7-1c19-4582-a87c-4f3fee4a0ee5,id=ua-c4c3e5e7-1c19-4582-a87c-4f3fee4a0ee5,bus=pci.8,addr=0x0 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on

Only aftermath is that in web admin gui I still see the temporary engine marked as "external-HostedEngineLocal" and I'm quite afraid of deleting it and having some effects on real engine one...