You would still need to accept friends for them to communicate with you so it shouldn't be an issue.
I pass someone on the street and it shows them my current username which also has my system code embedded (for ID purposes incase we pass again, and again and again), and some other useless stats, but he can't contact me other than to send a friend request that I must accept before we can have any sort of non automated communication through our 3DS'.
If we simply pass everyday, it would still identify me by my systemcode regardless of how many times I've changed my code.
for example, I could pass GamerX123 around 8:15am every morning and his 3DS would read passed BNM 3x @ 8:15
and even if the next day I changed my name to BlueBomber, the next day his 3DS would simply read passed BlueBomber 4x @ 8:15
if the service was exactly like steam, then maybe it would allow you to click the name and see that he may have previously known me as BNM
and if changed my name again, it would say previously know as BNM, BlueBomber and any other name change I may have had since we've been crossing paths.