Don't think Ford or dealer would be liable to honour warranty on a modified part.

Like Doo says, if you can be bothered to put the orignial bushes back in, and they don't notice, another Ford dealer may make a claim to Ford on your behalf, but if the original claim was made and rejected Ford will have a record of it.

But modifications to one part of the car don't affect warranty on another.

E.g. - if you put different bushes in the TCAs and the CD player failed, the two are unconnected and the CD would still be cvered. It all gets a bit wriggly when they MIGHT be connected - e.g. you fit your bushes and the gearbox goes. The makers will argue that the new bushes alter an angle for the driveshafts, putting strain on the box or similar bollox, leaving you to prove that the mod DIDN'T contribute to the failure.