I’ve seen this approached a couple of ways in the past. In one case, when I scout wasn’t able to obtain a resolution, he reached out to the scoutmaster. The scoutmaster then reached out to the MBC to find out what was going on. Ultimately, the issue was cleared up, and the scout didn’t complete the “extra” work that was being requested.
In another case, the parent reached out to the DE (whom he knew from church), who then “clarified” the issue with the MBC. Again, the scouts was not required to do “extra” work.
I generally think that avoiding confrontation is most likely to yield a better result. However, it is very clear that counselors can not specify which option a scout must complete, when the scout is permitted to complete “N out of M” equal subrequirements. If the MBC does not provide a satisfactory answer, I recommend reaching out to either the SM or another leader in your unit to assist your scout in resolving this. If they are unable to help, I would recommend reaching out to your district executive the chair of your district advancement committee, if you have their contact information. At the very least, the SM needs to know that this is an issue with this particular counselor so that they don’t refer scouts to the counselor in the future. The district advancement personnel need to know that the counselor is not complying with the requirements as written so that they can take corrective action with the counselor (generally just a reminder that the requirements as written, no more no less, is the standard). They might, however, have had previous complaints about this behavior from the MBC, and need to take different action.