Due to the complexities of the english language, irrespective of any dictionary definition legislation comes with its own definitions for keywords
However the meaning of ‘manufacture’ does not need to be argued as the VCRA covers both ‘manufacture’ and ‘modify’
Repainting or removal of paint would fall within ‘modify’ to the letter of the law, and the purchase of an IF followed by immediate conversion to RIF would in my opinion be an open & shut case in court.
With regard to UKARA, that’s not part of legislation in that the UKARA is an industry scheme that fulfills the legislative requirements
This is where the grey area comes in, you could meet the required ‘defence’ and be acting for the purpose of airsoft skirmishing which would then mean you can legitimately modify ..... and that would be subject to a case taking place to legitimise or disprove the grey area