[FE7] Support Disabling/Enabling

I was wondering if there is a way to start with supports disabled, then once a certain chapter is reached, supports are enabled. Almost like the transition from Lyn’s mode to Eliwood’s mode, except the “mode” remains the same and there is no “Lyn Mode Ending”. I want it so that no support points are gained until that certain chapter is reached, then allies can gain support points/support. Is this possible?