That would be quite difficult to accomplish. The time and effort required would not be offset by the fee that we are being charged. Also, adding usernames conflicts with our desire for players to remain anonymous. We work hard to avoid links between a player's username and their real-life identity. Having said that, you could get an aftermarket product or service to do this if you really want to do so - and if your parents think it is acceptable.
I was actually thinking about doing this on the sleeve for myself . There are several places online that you purchase actual name patches and iron on printings for under $10 even. If you have access to Amazon there are some reputable companies within the 'PRIME' family or if you google around with your parents guidance you can find them elsewhere (just be careful for scammers). I know there is paper you can buy that you can print them yourselves and although it works, it is usually best on a white shirt. The color of this shirt may not produce the best results. I worked for my parents screen printing company for a number of years...I can still tell the difference between the material blends of shirts by touch, it is not a glamorous trait i assure you! BareClawz
There is a paper product in the printing or craft sections of your local mart-type store that makes iron-on from your printer! You could make you irl or username, then maybe get a grown-up to help iron it on. Do use thick cardboard between the shirt to shield the sandlot logo tho, or it will melt. Or add your name on the sleeve.
We got ours in the mail today....the colors are very pretty irl! I don't usually like to advertise on our clothes, but for Sandlot I am making an exception .