is it possible in any way? the only variant i found is by making copies of units with edited build-times and obj names, plus change of commandset for construction building, exchanging "old" units with "edited". but maybe there's some other way?

It's the only way I think.

I'll have a proper dig when I get more time, but the Remix mod does this with the tank (and others?) general.
Seems to work by piggybacking or reusing existing upgrades.

Specialize this Warfactory to the production of a single unit type.

Specialized units build twice as quickly and at half the cost.

CommandButton Tank_Command_ConstructChinaTankBattleMaster_Specialize
Command = OBJECT_UPGRADE
Upgrade = Upgrade_ChinaOverlordGattlingCannon
TextLabel = CONTROLBAR:UpgradeChinaSpecializeBattleMaster
ButtonImage = SNWarMaster
ButtonBorderType = UPGRADE
DescriptLabel = CONTROLBAR:TooltipUpgradeChinaSpecializeBattleMaster
End

Upgrade Upgrade_ChinaOverlordGattlingCannon
DisplayName = UPGRADE:ObjectUpgrade
Type = OBJECT
BuildTime = 15.0
BuildCost = 300
ButtonImage = SSUnitUpgrade
UnitSpecificSound = OverlordExpansion
End

Theres probably more relevant code to this, but its late and this may get you/others on the right track.

actually i accidentally found solution with creating obj that has little part of code of targeted unit, but with changed build time + BuildVariations that point to original unit.