Male 21y 5'9" 187lbs, 365 S/300 B/440 D

I've been lifting for the last 6 years and I'm thinking about going out for my first competition in November. I was following a Wendler program for a few months but I started to plateau so I started a 4 day CMS-MS Prep Sheiko program for the last week and a half because I've found that higher volume workouts work better for me, and I'm hoping to add 20lbs to every lift before November. My question is that while the program is M/W/F/Sa, is it harmful to do light accessory work on T/Th? For example, since Sheiko doesn't have much in the way of accessories, I was thinking about doing a few shoulder exercises on Tuesday, and maybe some arms on Thursday, just to preserve some of what I've built over the years