What will infantry school be like as a prior service SGT from the marines that already has a combat deployment under their belt goin army ?

Just yell “oohrah!” a lot.

A mistake!!!

What will infantry school be like as a prior service SGT from the marines that already has a combat deployment under their belt goin army ?

A cakewalk.

Ah, I've read a few responses that indicate you won't receive special treatment from the
army. On the other hand, your Marine training will get you lots of gold stars. Furthermore, your platoon mates will recognize your devious Corps training and will follow your lead. I had my squad marching to commands like "Hippity hop! Group stop!" You'll do fine, Marine as long as you remember that's what you are: a Marine.

From a Senior Officer's perspective, it would be my expectation that my TI's/DI's/etc. will take advantage of all the resources they have in any particular class. You are one of those resources, and I recommend that you present yourself as one, when the question comes up (but only if the question is asked). Otherwise, you should have some advanced skills (or, at least some skills that a slick-sleeve or one striper won't have). Use them if they apply or will help somebody else.

So the Active Duty transfers and the reclasses comming in via 11 Series are treated with respect their current rank gives them to an extent. The Army has a philosophy that if your in an Army School you are treated as rankless but at the same time, you having earned that rank they are not going to dog you out or wolf pack you unless you do something arrogant in front of the recruits. They will brief you when you arrive on the dos and don'ts and potentially the expanded liberty they will give you that the regular recruits do not have (I don't think they will restrict you to barracks after hours like the regular recruits). The biggest thing is they kind of want you to mentor but at the same time do not get between the DS and the new recruits nor boss them around as your an AI or something. If they ask you dumb questions about combat, you do not have to answer them but you shouldn't be a jerk about it either. Also, don't debunk the mental stressors the DS impose on the new folks. So that's it in a nutshell.

As for when they will insert you into the 22 week program. They will obviously skip week 0 and week 1 because you will have your issue already and know all the BS they cover in those two weeks. However, it is up to the replacement center what makes sense and what is available. They want you through the training as fast as possible vs hanging around. So you could get start of the program or half way through. It helps a lot that you have updated rifle qualification and PT test scores in your Active file before the release.....so that is an advantage because they can look at those and be confident of where you are in those two areas.