I still think this whole copyright-my-bend thing is fraught with litigation danger from the manufacturers of the equipment you bend - especially if you draw and cpyright a schematic and show part of the manufacturers device's circuitry in it, or how to hook it up to a diagram of the device without their permission. I know for sure that Roland are vigilant at sending out cease and desist warnings to people that design things that even look vaguely cosmetically like some aspect of their equipment, let alone functionally attached to a part of their circuit.
SCAT: the safest thing for you to do, in your situation, while you are still a small outfit, is to write to Roland Inc. (or whatever brand of device) and ask their authorised permission to use their circuits to add your own bends to theirs for the purpose of selling their machines modified, explaining exactly what you are intending to do. Then see what they say. After all, wouldn't you expect that from someone wanting to copy/modify one of your designs? Then you will know for sure, and not be taking guesses about whether you are in the legal right or not about coyrighting an attached circuit.
One of 2 things will happen:
1. They will give you written permission, with certain limitations and obligations
2. They will send out a cease and desist letter and threaten legal action
If they send you a cease and desist letter, stating the legal action they will take against you if you continue, it will then mean that your copyright-my-R8-bend circuit idea is invalid. The only way to know for sure is to ask them what they think of it. I'm betting circumstance 2) will be what you get.
If you DO get that warning, you can still gain comfort from the fact that you did the right thing by asking them, and that you know exactly what you can and can't do, and that the business model you are working on should be changed while you are small enough to not suffer significant losses. Ditto for any other manufacturer you alter the circuit of. This is how bona-fide real businesses go about these things. They cover their legal asses by communicating with the party concerned. So if you consider yourself a business, not just a hobbyist making a few bucks on the side, you should dot your legal i's and cross your t's early on in your commercial history.
If it turns out that the copyright-your-bend assumption is false, you could still continue selling bent stuff commercially if you kept your head down and not bring attention to yourself by attaching copyright claims to your gear or advertising that clause. It really makes you a red flag to a bull for the big companies. And just because the UK has certain copyright laws doesn't mean Japan has those same laws or opinions, even in a different country, and that they will respect them and not go overseas to fight a legal battle.
Cheers, Graham