[thatguy96]

3) I believe in WinSPMBT that you can only dig in infantry and emplace vehicles and artillery depending on mission type, such as being the defender. Infantry may dig in if left alone for long enough, can't remember. Trenches and the like stay around though during defend missions so moving infantry back to trenchs or into sandbag emplacements and leaving them static digs them back in (if your units were chased from their positions or you otherwise moved them).

4) You can rework an OOB in the game entirely, as to represent another country, but the tools available to the consumer do not allow countries to be added.