stainless bolts

taking the back brake plates off on my series 3 , for painting whilst doing brake pipes etc , is it possible to replace the 6 bolts that hold on the plate / stub axle to axle with A2 stainless ones?

So how does your question to an engine?
As for “is it possible to replace the 6 bolts” you can tell us when you have done it, if wish to know if it’s okay to use stainless bolts, then... yes.

Personally I would stick with the originals you would not want them coming undone when driving.

I wouldn't use A2 "stainless" - A4 maybe - BUT, I'd be checking the tensile & shear strength before contemplating it - if you stood on the brakes and the bolts sheared ..... it might get a bit awkward

A2 isn't really stainless enough ..... probably better to use the originals, and copper slip them and then wax protect it all afterwards

And ..... @northern scot - it'd probably be better to take your postcode out of your location - the city where you live is plenty good enough as a location

According to series 3 parts book they are 3/8 BSF LR Series are selling SS as OEM
https://www.lrseries.com/index.php?route=product/search&search=237340
paddocks similiar price but look zinc
https://www.paddockspares.com/90576510-bolt-3-8-x-1-1-4-bsf-thread-h.html

Don't. Use new originals. Thread lock will protect the threads once fitted. These hold the hubs on the vehicle. Stainless is very different to steel.

Most "normal" stainless bolts will shear much quicker than the steel used in the original bolts.

Good idea, but it won't work in this application.

And stainless threads love to "pick - up"
Nightmare!!
I am a metal worker and love using stainless for lots of things but not for threads . Be warned they need plenty of lube.