It is possible to increase the level of memory page sharing on a cluster above the 200% with a option and start the vms after that change ? or it is possible to deactivate the memory threshold with any option?
First, let me be clear that this is complete speculation. That said, my interpretation of these features based on how the GUI behaves is that the Cluster Memory Optimization (CMO) setting changes the default Physical Memory Guarantee (PMG) on new VMs under the Resource Allocation tab. However, you could set that number manually to whatever you want. I have been setting it to 1/4 of the Memory Size (MS) on the General tab as a general rule, but varying it by VM as needed.
So, to restate, when CMO is set to None, PMG=MS when creating a new VM. When CMO is set to Server, PMG=MS/150%. When CMO is Desktop, PMG=MS/200%. But you can still set the PMG to any custom value any time the VM is not running. That much I am sure of. What I have not tested is my expectation that the engine will pile the VMs on the hosts based purely on their the greater of PMG and actual VM use. It would be reasonably plausible that the engine limits VMs on the hosts based on CMO as well as PMG and actual use, but I just don't know for sure either way.
I would greatly appreciated it if some guru could school me on this point.