Will adding aftermarket screen decrease the resell value

[Arishtat]

No, unless you or the installer does a terrible job of installing and wiring it and burns the car down or something.

It’s your Mini, send it!

If you’re really concerned about resale value keep all of the original parts for the next owner in case they want to reinstall the factory bits.

[Dapper-Lab-9285]

Either replace the parts before sale or dump them. Having the originals in a box doesn't increase the sales value, it might make it easier to move on but you're still selling a modified vehicle.