This was already implemented. The last radio relay station at a base cannot be dismantled unless there's a dismantle base order in place at that base. It works fine from what I've seen on Conflict HQC, I haven't tested it on Conflict Legacy though.

There is a problem with the pre-placed radio relay stations on Control Points (purple objectives), where they can be dismantled by anyone at any time (your own team, the FIA, the enemy team, doesn't matter if they're capturing the objective or not). See AREXP-65.

Right now the best strategy is to replace the pre-built FIA relay with one of your faction as soon as you capture a purple objective, then it will be protected by the anti-griefing script.