personally I wouldn't trust anyone to do that mod on my behalf, but each to their own. If you aren't competent to work on brakes, then dont work on brakes.
Certainly other than circlip pliers, no metal tools should be used anywhere near the m/c bore or internals.
The seals need to be carefully inspected, even if "new" and you need a VERY clean area before considering opening up the m/c.
For negating the non return valve, various methods have been used by many people including making a small hole to complete removal. If a small hole is enough to prevent disk brake pressure retention, then why do more (IMHO).
For reassembly, if you don't have brake fluid seal lube (usually white and nearly impossible to get) then don't lubricate the seals with anything other than the correct brake fluid!
Even if you dont modify, I tend to disassemble 'standard' Minor brake cylinders (wheels or m/c) and inspect before fitting! Rolled seals and swarf are not what you want to find but it's better to find (and rectify) a brake problem with parts on the bench than in a ditch.
The last "new" m/c I fitted without checking was problematic. This was a Lockheed part (previously AP, now labelled Delphi - but not really 'original spec' other than the looks) as I'd heard many bad things about the cheap copies (which were approx half the price, but deemed 'not worth the risk' by many of the parts suppliers, although still selling them).
I never managed to get a good pedal, and a month later another competent Minorist also failed to improve the pedal travel. About 5 years later the m/c was changed
again and that cured the issue
