If im reusing spokes and have a rim with an ERD of 528mm, theoretically with standard or longer nipples etc what rim size can I get away with?

Anyone for the late shift?

Sort of depends on the original build
Did the builder go a bit long or short or is it bang on
and which way relative to that that you are going with the new erd
What rims are you using ?

Std specialized roval dh rims. Trashed after a few runs would rather run 721s which are 535 as I have a stack

That’s gonna produce a difference of about 3 mm in spoke length
So You might be ok but as I said if you have a build that’s a bit on the short side you might not
Have a look in the rim to see how far the nip is wound on to the spoke

If you’ve got 12mm nipples you could swap to 14mm to get you 2mm. Haven’t worked out the numbers myself so can’t confirm 3mm is all your going to need though.

Spokes typically come in 2mm increments, so +/- 1mm after rounding is accepted norm. If the rim ERD is 3mm bigger, then 14mm nipples will give you 4mm, so you’ll have a little bit of spoke showing through the nipple. If the rim ERD is smaller, it should be OK as about half of the spoke/nipple thread is redundant anyway – thread loads only taken by about 3 turns.