When you increase the target loyalty with the switch, the AI will garrison provinces better and generally become more stable. Not only will this reduce the chance of rebellions, but it will make it harder for the various AI factions to beat each other up. The 2 main causes of influence drop are losing provinces and attacking allies, more stability will keep this from happening as often, and this will last throughout the game. Changing the faction leader stats in the startpos file just changes the stats of the king at the start, heirs will quickly revert to the mean as the game progresses. Except the Byz, they get a built-in bonus so they will usually be higher.