The SLAM-ER will function differently than a TLAM, but will still be capable of ground attack.
Keep in mind, this missile has been broken in stock DW since 1.0 and up to 1.02, so there are essentially zero missions that use the P-3C in a ground attack role requiring the SLAM-ER.
No, I cannot change weapons because that is hardcoded in the interface for playable platforms, I can only change their parameters, and no I can't make dubs. It's either all the way changed or not changed at all.
If I could simply swap weapons in and out, well, then this would be a whole different experience modding this game (think new playable platforms...).