You'll want to spray with a suitable protective paint afterwards or coat them to prevent rusting... I'm chopping up a subframe to remove unwanted bits, of which there are quite a few- though I'll be leaving the rails, they're quite handy. I use the RHS one for luggage and the left has the shock reservoir bolted to it
A straight subframe can be had for under £40, usually, so if it does affect value it'd be simple to change it back.