If I remove a shimano FH-M525 135QR from a wheel and replace it with a FH-M788 142x12mm, can I re-use the spokes?

Depends if the flange spacing and height is the same, search out the tech docs on the shimano site.

FWIW re-using spokes can make the build a pain in the rectum as they all stretch slightly differently, ditto the rim. I did it once to practice wheelbuilding and it was a royal pain compared to just starting with new spokes and a rim.

I had a look on the shimano website and they all do have the same spacing and height.

That makes sense about the spokes all stretching to suit the rim, this would be my first wheel build so maybe not the best idea to re-use

I’ve reused spokes loads of times with no issue.

Back in my teenage days of maximum bike OCD-ness I’d often dismantle my wheels just so I could properly clean & polish the hub flanges. I must have rebuilt those wheels dozens of times.

e days of maximum bike OCD-ness I’d often dismantle my wheels just so I could properly clean & polish the hub flanges.

Oh my!

I’d often dismantle my wheels just so I could properly clean & polish the hub flanges.

😮

I use this website for working out spoke lengths. pick a rim and try using the old hub and then the new hub and will tell you if they are the same length

http://www.prowheelbuilder.com/spokelengthcalculator