if the OP literally wants to know would people be bothered, how do i put this, the odds of people being irked probably rise as either the town gets smaller or the town gets better at running. if the town is small enough there is nowhere to hide and a pseudonym can't so much hide you as make things awkward. and if the town is better at running then people will be annoyed. the premise seems to be the town is big enough one can hide but yet somehow has no other good runners. but if you're already anonymous in a big town then why do you need the disguise. and to me the bigger the town the more the odds go up you have underestimated some mix of the other adults and the new kids coming up. [i always thought people's hopeful theories on how their college sports experience would progress neglected that the coach is out there recruiting more people for next season, and for 2 more years after that. you work on elevating your game but the coach makes his own moves......]
personally i moved back to my hometown after college and for the whole decade i kept bumping into or playing against old soccer teammates and opponents the whole time, and that's a big city.
it's also a static view of the community. you can maybe hide one race. afterwards, if it goes to your dreams, people will want to know who you are. even if they get a fake name your fake name would develop a reputation the 2nd, 3rd time around. i think that would be true even someplace like NY. it's a subset of a subset and people start to know who you are.
i am still asking, "why?" and it's not to be a jerk, it's an interesting angle at self-analysis. and i don't mean the superficial, first answer for why. i mean why do you want to interact with this town this way. or why do you think of yourself in a way you want both dominance and yet anonymity. it's kind of batman and batman's not normal.