well i would never install data protecot into the c drive... i remember some years back when i've spoken to a dp teacher he also told me best practice is not to install dp on c drive. (file system fragmentation, performance and so one) every installation i do, i have an additional disk for example E drive and install it there. (E:\Omniback - no splitting between programdata and program files)
no there is no problem using the omnidbutil -change_cell_name. used it often, worked fine.
well if you decide to install dp on the new server into a different direcotry (as i mentoined above) then you cant just copy folder db40. you have to export the idb
omnidbutil -writedb -mmdb <path> -cdb <path>
on the new server you can do your installation into e:\omniback. then check that you have enought fnames and extension files for importing the idb again. if everything is alright, you can do an omnidbutil -readdb -mmdb <path> -cdb <path>. then do the change_cell_name. then you have to relocate the dcbf (Detail catalog binary files) directory. i think that was already discused in the forum...
this is a way you could do as well. but then i would suggest update existing cell server to 7.0 -> 7.03 and leave it running several days to look if everything is fine. then migrate. otherwise if you update and migrate the same day and you have troubles on the new cell server, you wont know if they come from the migration or the version update.