Im looking at installing a screaming eagle heavy breather (29264-08) on my 07 xl883c ( upgraded to 1200cc).

Already have the S/E air cleaner stage 1 and S&S slipons, and a SERT and been remapped.

Will i need to remap agin once i fit the heavy breather or should it be ok with the previous mapping ?

i think you will have to remap it -it is a much bigger filter!!
but you can fit it and just check your plugs if no backfiring/popping and plugs are ok -all good