From rules perspective everything is simple: you don't have to demand credits or Ore prior to attack; it's pretty simple since you can demand literally everything. The fact that Molly roleplay allows them to pirate BMM miners is just an additional opportunity that isn't avaliable to official Gaians faction according to their lore (while both Gaian and Molly regular and Guard IDs allow to 'demand credits or cargo from traders and unallied smugglers or factions').
From roleplay perspective it's even simpler: while you fit the minimal technical requirements with your 'demand', you can do whatever you want - take miner's cargo (full load or just the part you can take - by the way, that's not a bad idea), take his ship by pieces, force him to roleplay (since people sometimes put more effort into such activities with a Supernova aimed at them), and if he calls in a Battleship - take a hostage and escape the place. Or you can just leave if the miner was that good.
The funny part is - when you try to play good instead of 2milordaiing, people notice it sooner or later, become better and start roleplaying with you instead of running and yelling - or they run and yell, but do it with talent. Bring security, bring escorts, bring something to make gameplay better and neither Gaians nor Mollys will be a that big issue making player behind the BMM character sad.
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Uh, and I'm so looking forward to Bretonia finally doing someting with the IMG openly helping the separatists in their hard work. Uh, =MMC=, [Garda], [MS], [MR] - this is all the same thing - damn Molly separatist, enemies of state, that use their profits to undermine the economy of Kingdom.