Exhaust crackles/pops on downshift but only when cold

Iv recently fitted a decat stainless manifold and done a backbox delete and iv noticed if i rev match right on the downshift it will pop now it only does it when cold and I know there's speculation on it causing harm to the engine but is there any way to do this when its warm also, without having it tuned to do so(havnt got time to have it all turned correctly at the moment)? Would it just involve some form of overfueling? Already running v power so not using the cheap stuff, any help is appreciated.