not sure where this idea of vosa looking to eliminate modfifications is coming from, cant think of anything in the test where this could be a problem.
i put a very nice, full custom car through an mot last month, passed with flying colours...this car was built from scratch but followed all relevent legislation.
vast majority of new legislation dont even apply to older cars, not seen anything creeping in that will change this.
in the future, as an example, i can see a day where if a DPF was fitted at factory, it must be seen to still be fitted and functional..if ever that happens, then chances are, going on vosa policy over history, it will only apply for cars from date legislation was introduced..end of the day, these DPFs are only fitted to comply with euro legislation that the government signed up to, nothing to do with vosa at all at the moment, but as removing the systems becomes more common, can see the government forcing vosa to take action.
as for bi annual mots, speaking [or should that be typing] as a mechanic, think thats insane...i could give a endless list of cars that are regularly and properly serviced, yet still suffer from dangerous faults in between, only need to experience the diabolical state of the roads to know what could happen...apply the bi annual to the owners that carry out bare minimal repairs/checks, which probably far outnumbers the owners that do it right, you end up with a lot of death traps on the roads...from experience of crash recovery, its normally the innocent that cops it..if anything, there is a case for 6mth tests instead of bi annual
There was an article not too long ago saying they were considering banning all vehicle modifications from manufacturers standard.