Probably, yes.  In this specific case, given its exceptionality, probably sed s/userCertificate::/userCertificate;binary::/ suffices.

I think i tried that at the time (it was a while ago), if i recall that pushed the line length above what was parsable, but if i manually would have re-justified each line length the lines would have parsed ok, but it was a large file and i was just giving it a quick test.

Does slapadd enforce a strict maximum line length ?