It's an interesting topic, which I've been watching for a while now, I do own a highly modified Mini, but it was done by a company back in the late 60's, I have the documentation to prove this, and the V5 is correct, however if I got stopped at a roadside check I wouldn't have all this with me, so no doubt I would have to prove that the mods were done before the rules came in, which may involve presenting the documentation to the DVLA, (and now that've shut the local offices that would be a trip as I wouldn't send the originals throughout the post) or a trip to a VOSA station to present it all. Would I spend ££££ changing a car in a way that these days might result in an IVA, probably not, however there must be a way of checking modifications (by an official body) without having to make the car comply with all modern safety requirements, but again this throws up problems of liability if the modification fails, so we are back to a MOT style test where the the modification is check once and declared safe 'at time of test' and the mod is recorded on the DVLA records and then shows that it's been looked at at subsequent MOT's
You will be fine mate.
Roadside tests would not cause you an issue as your V5 is correct. to be honest they are very unlikely to be interested in giving you hassle at the roadside unless you are drunk or uninsured etc etc.
The computerised system is where the "human" common sense has been removed. Garages (some not all) are getting scared of the rules and are going above and beyond to protect themselves with the check boxes.
My de-seamed van with a roof chop had a note on the advisory page that the roof height had been lowered in both 2011,2012 and 2013.
My V5 states special bodied and also has a note in the front section of the log stating that its rebuilt from parts some of which are not new.
Im sure someone has seen the mot notes and checked against the V5 every year and can see its all correct so they have given me no hassle.
I contacted DVLA about fitting non original from panels to my elf as they are no longer made. I fitted a clubby front with the inner wings and they were more than happy for me to go ahead.
I did pop it over to VOSA as they asked to see it once completed.
The inspector said that forward of the shock mounts he considered the panels not parts of the monocoque safety cell structure so wasn't concerned.
This may be on a person by person approach so don't go fitting fibreglass fronts and brace bars without asking first.
With sensible planning and a few questions at DVLA and VOSA I'm sure we in the mini scene can carry on with most mods.
I understand the frustration of some members on here about the dangerous mods and in some cases even the death traps. Just ask first and allow the extra money for testing within your build.