As I understand, UKARA is not a defense, but a very convenient and widely accepted way of proving a defense. Airsofting itself is the defense, right? So:
Is it legal, having attended a single skirmish, to strip any paint off a two tone IF to restore it to an RIF?
Is a photo of you airsofting and receipt details of a site booking enough to prove your defense? I thought yes, just checking as to not bring the sport into disrepute. Thanks in advance
Actually, UKARA is more a case of being a very convenient way for
retailers to provide a defence for having sold a realistic looking weapon to someone, and for us, as buyers, to more easily prove we are legit when buying a RIF; so yeah, it's bugger all to do with the law.
If you have been at an airsoft site often enough to have filled out the forms for a UKARA, then
the mere fact that you have been there often is actually enough of a defence, even if you never filled out the UKARA application, since you could simply ask the proprietors of the site to vouch for you (and in fact, the UKARA scheme is simply an organised way of having airsoft sites do this for the benefit of the retail trade), but the CPS could simply check any airsoft site's records, and if they found your name on the site's books a few times, then it would be apparent that you were at least attending airsoft events regularly. If they found your name listed once, then I doubt they'd take that to mean you were a regular airsoft player, any more than going to one footy match would make you a diehard supporter of a club. Thus the law is, as always, open to interpretation and often the plaything of some clever wording from a barrister for the benefit of a jury.
So the very fact that a UKARA application expects you to have been to
three airsoft events, minimum, and these
over a period of at least two months, is intended to prevent someone who is merely looking for an excuse to own a RIF from simply rocking up to an airsoft site, throwing fifteen quid at them to attend a game - making that payment a matter of record - and then never going airsofting again. We may not necessarily like the UKARA system, but it was at least fairly well thought out in terms of preventing that sort of abuse of airsoft sites, in not providing an easily-abused excuse for any idiot to simply go once, buy a RIF and then be a d*ckhead with the thing.
And beyond merely having a RIF, it's particularly important to have a credible defence for having 'manufactured a RIF', as the act of doing this is specifically mentioned in the Violent Crimes Reduction Act as being a bit suss unless you have a legitimate reason for having done so. Simply having attended one airsoft event is hardly an ironcast defence for this, and I personally would not want to rely on that. Whilst it should be borne in mind that it is still the burden of the prosecution in any court case to prove any intent upon the defendant's part to commit a crime, the better you are able to substantiate your legitimacy, the safer you are from bogus accusations of criminal intent. Thus the possession of a RIF alone does not mean you are going to hold up an armoured car in your local high street any more than having a kitchen knife in your kitchen means you are going to stab someone down at the local boozer, however, going to the extent of making a RIF, and then of course possessing that RIF after you have made it, is
two boxes ticked, and that means making an accusation stick will be a little bit easier, as it shows you were 'planning' to do something, and the CPS love sh*t like that, because the word 'planning' always sounds devious, although you should bear in mind that the law is not
trying to catch you out, if you are legit and can prove you are, then it's all good. It just makes good sense to ensure you can easily do that, and acting responsibly helps us all.
Just go to a few games and get the UKARA. It's not that much of a pain in the arse to do.
but thanks, I'll go to a few games then strip 
