Ah, great you thought of that!
However, I think it shouldn’t be a problem. You can change the amount of XP awarded by using these statements:
constructible_constructxpbonus <value>
Give ‘value’ amount of XP to the player that finishes the construction.constructible_destructxpbonus <value>
Give ‘value’ amount of XP to the player that destroys the construction.
I’d just set them to zero.
Ah cool 
Thinking about it, the flag MG in railgun is sort of like this (except it faces in a different direction for each team, I’m guessing using two overlapping sets of entities faked to look like one, same goes for the command post on that map) and it gives out the correct XP so it must be possible These don’t let the building team destroy what they made though of course. You could have some kind of ‘self-destruct’ switch that only the building team could press to trigger the constructible to be removed (maybe after a 5 second delay using a timer to let you get out of the way :)).