as long as all the materials are MCS compliant it can be done, but the paperwork trail is almost identical. Alter to suite, like formal quote will be 'fit only' or words to that effect, SAP won't be applicable, put note in file etc etc. If you are installing you will still need warranty.
I've done this once or twice, to be frank it's such a PITA I wouldn't be inclined to do it ever again, plus most of the margins are in the VAT return, and if you haven't supplied materials, that's quite a loss.
I did once have a major argument with a fella who was so clever he had bought and installed his own system, and wanted me to sign his installation off. I refused on the grounds of legal liability and quality control, and he got all irate! His shed with the panels blew down a few months later in the first major gale of winter...... :slap
