Hi @Tipenso ,
If you are talking about GUI, you'd need to modify PVE code to get the default value changed. Going forward, you'd need to keep that modification in place through PVE upgrades.
It would be interesting in future versions, to be able to vary that default value in the migration options.
I had thought about the 'max_workers' value, but I read somewhere that the GUI option 'Parallel jobs' has a higher priority.