its a reshell if ur using the orininal tag from the rst or goin new reg

a reshell is just changing the shell of the car it would still be an frst unless u keep your new peg plates and insure as a kitted 1.1 (cheapy cheep)

a full rep is using all the rst bits and using the tag from the new car,

to be honest mate ring companies tell them your plan see what happens

i got insured on my ERST at 20 + 2yrs NCB for 700 quid

but it depends on how u feel about breaking the law..