Etype mech fitting

Can i fit a new un without taking the old one off totally – leave the plate on and bolt the new mech onto it?
Not got a self extracting bolt on my xtype chainset – can i use a normal extractor on it?

my (largely uninformed)answers are
bolt new mech – yes assuming you have bolts and it is EXACTLY the same size /as the replaced one – otherwise what if it hangs too low and hits cogs on changeovers etc ?
Assume you can use a normal extractor if you can thread it in to the x-type but dont know if you can as never tried.
I have an E type mech you can have for postage if any help.

i have 2 etype mechs here cheers – hence trying to swap one cage over to the older plate whilst its still on the bike. Will have a bash and see what happens