It isn't different, the prep will be identical for either, it just depends on how much prep you want to do to get it perfect beforehand. I would prep the parts the same if covering in paint or plastidip, ask any painter. Platidip will not make your gaps come out correct, or fix low/high spots. Only hide them better since it isn't glossy and finishes in orange peel, which in the plastidips case, cannot be color sanded and buffed out. You would also finish in 400grit prior to spraying, which is pretty typical across the board for no matter your top coat. Since gelcoat is fully cured, you only need to rough up and can go right to laying base color. Super easy especially if going same color as your gel coat.
The only point I am trying to make, is that painting is not that hard. Sure, you could save a couple hundred bucks maybe with plastidip. But, will lose thousands on resale. Not to mention the skills that will be learned for other parts of the project, or future projects.
I am a very firm believer in the saying, "if you don't have time to do it right, how will you ever have time to do it over".
If there is only a few spots that need to be touched up on your car AJ, you might be able to get a small container of the gelcoat in matching color, and spray, brush, roll it on and sand smooth and buff. Cheapest, easiest, and best finish outside of painting it entirely.