We all know starters are not being used as intended in RS right now. Hell Movie just put in his video yesterday telling you if you aren't using Kluber as a 3 inning save guy, you are using him wrong. That is an issue. Starters in relief need to be an EMERGENCY decision, and there needs to be concequences for making that decision.
First, Non relievers brought out the pen should be taxed 1.5x to 2x per pitch when brought out of the pen. They aren't used to coming in mid game and this puts them out of a comfort zone. Then if the starter was not at full stamina when brought in as relief, following the game, you should incur a 1 game penalty before stamina regen begins. Also keep the current system where pitchers must be on the active squad for stamina to regen. These 2 changes will make it so you'll have to pay the price in future games if you choose to bring that starter in for a relief appearance.