They have no mention of a discount for trading in
Apple Trade In - Apple
That said....if you do choose to use Apple’s third party partners for trade ins, document and take photos throughly. There are more than a few posts here from people claiming to have the recipient claim a different, usually damaged, condition of sent in devices as opposed to the condition the owner claims it was in.
I looked on Best Buy’s page for trade in and randomly picked a pro model and good condition and there was no option to say that it was engraved. So it may not be an issue, at least going by that. (Personally if you do trade it in, and you’re in the US, I’d recommend Best Buy or selling it yourself outright. I’ve used Best Buy twice for my devices, I take in the old one, get a gift card, buy the new one and take it home.
Or if you do trade in with APple, I recommend that you only take it into an apple store and do not mail it in.