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