There is nothing to stop you from paying for one by-law and then allowing other owners to use that as the basis for their by-laws. But asking a lawyer to provide you with one that removes their opportunity to charge several times over is like asking turkeys to vote for Christmas.
That said, there are reputable legal firms that will provide a standard by-law for a one-off price. They make their multiple charges by being one of the few around who do that. Just Google “standard strata by-law” and see what pops up.
While we’re here, it’s worth noting that it’s your owners corporation that approves the by-law and no one else. Provided it doesn’t breach strata law or any other law, it can say what you want. If it doesn’t, you don’t pass it.
The valid reason that a lawyer might strongly recommend you have specific by-laws for each application is that there might be significant variations from bathroom to bathroom that are missed by an off-the-peg by-law.
For that reason, your standard by-law should have a set of adaptable inclusions and exclusions, or at least a clause covering all eventualities. After all, the by-law is there to protect all the owners in the building and, most importantly, to legally transfer the upkeep of affected common property to the renovator and any subsequent owners.
As for what to say to XYZ Lawyers to get them to provide what you want, just say “if you won’t do it I will get someone who will”. Neither they nor the strata manager can force you to do otherwise.