Hi David ,
This is no problem , if your number plate is a stick on type (ie no visible bolts) simply gently prise the plate free of it's adhesive strips/pads , if it's secured by bolts/screws undo these .
The "surround" be it a black painted one or stainless steel is normally held on with 6 "pop" rivets , drill the heads off with a 3mm drill bit and the surround will come off , once off carefully drill the remainder of the rivets out .
To fit your replacement you can rivet it back on with a rivet gun ( cheaply obtained complete with rivets from car accessory/diy store) One thing to bear in mind is that some of the genuine Jaguar surrounds take a larger than standard number plate , the width needed is the standard 20.5" but the height is a little under 5" so buy a plate from someone like
https://www.aplates.com/aplatesshop/platebuilder.asp and sand the bottom edge so it's a really snug fit in the surround .
If you fit a "standard" rear plate to the larger Jaguar surround I think they look a little odd but thats up to you

, I prefer to secure the new plate with self adheasive strips rather than bolts but thats a matter of personal choice as well ,
Hope this helps ,
Nik