Laws here do not enter into these intricacies
Neither do they, here; they're actually quite vague. That's why we have the Bureau of Alcohol, Tobacco, and Firearms, which creates regulations that *do* define the specifics like I've described above. It's probably the same sort of situation in your nation as far as the local regulations part. Open-bolts were once legal here, but were ultimately found too easy to convert to full automatic; if that is not yet the case for you, you'd be able to use very simple open-bolt semi-auto design solutions (many to choose from).
Since I assume that in your nation, like ours, the penalties for illegal machineguns are severe and prosecution aggressive, it's really best for you to consult with a local expert to make sure you're approaching this the right way (and also find & review the pertinent statutes). What's sad, is that because THR is US-based, we probably can't really discuss the technical particulars of open-bolt trigger systems that would be highly illegal here. The "NFA" (national firearms act, the law governing this stuff here) firearms subforum here or elsewhere would be better informed, and more likely to be authorized by the moderators to help you out. I'd PM one of the NFA forum mods here to see if they would be okay with you asking the question in a publicly-visible area (due to liability and gun politics, many folks are uneasy discussing these items, even though the information itself is legal)
It's even worse for import/export regulations, since you have not one but at least two nations' regulations making things difficult, if not impossible.
BTW, I wouldn't emulate the PM12 if I were you; Beretta put like a dozen parts in that trigger system. The Suomi and CZ26 have like three parts by comparison
TCB