If I could change one law with respect to "things Boston could relax on" I would lift the Commonwealth-imposed cap on municipal liquor licenses. Let the cities and towns decide how many they want to permit. Having the Commonwealth decide this for them makes zero sense. The enforcement of liquor licenses has a place in our society; caps on liquor licenses set by the Commonwealth and not the individual cities and towns do not.
So many of the issues with Greater Boston's social scene follow directly from the Commonwealth restricting how many liquor licenses can be issued. It makes everything more expensive (including food and drinks); pushes small, funky, independent bars, clubs, and restaurants out of the market; and turns every establishment generic, loud, and overcrowded. It's really hard to have a cool little music venue or a chill neighborhood (quiet) pub when there are only a set number of licenses to go around and everyone needs to compete for them with huge bars and clubs that will pay six-figures plus.
The laws hit Boston particularly hard (Boston gets fewer licenses per capita than the rest of the Commonwealth because back in the day Beacon Hill didn't trust the Irishmen that ran the City with alcohol) but other cities and towns also suffer. Some have tried to get around this cap (
see: Cambridge) but have done it in insanely unfair and backwards ways.
Most of the opposition to expanding liquor licenses is born out of the cap on licenses itself. For one, existing holders of licenses paid a ton of money to get theirs, so they don't want new competition to have a competitive advantage by gaining access to new licenses for less. I'd propose a gradual increase in licenses over time, with the fees for newly issued licenses used to "pay back" incumbent license holders. Additionally, the NIMBY public pushes back on license increases because they look at current license holders and see loud, obnoxious bars and clubs and decide that they don't want more of these in their neighborhoods. The thing with licenses is that the loud obnoxious bars are the first to procure them (they have the highest willingness to pay) while the quiet neighborhood places are the last to procure them (they have the lowest willingness to pay). Thus, more licenses mean more quiet neighborhood places, not more mega-venues (i.e., the mega-venues already got theirs, the quiet bars haven't). Travel around Europe and there's a little cafe serving wine on every corner; this is because they don't have license caps in most of Europe. In Massachusetts, this is illegal. Even in other US cities where licenses are easier to obtain you find way more "quiet bars;" Boston has
very few of these. And even if you do support a cap on licenses, there's no reason it should come from the State and not the City.