Follow this link
and use method 1 to change the carrier name on any rom you are currently running.
[NOTE] It is specified for the optimus V but it does work for the evo 3D
Here are instructions however from that site on how to change the carrier name:
Method one: Only allows 17 characters
1) Put the ROM.zip file you used to flash your current ROM on your computer
2) Right click and choose Open Archive (I suggest using 7-zip
3) Navigate to /system/framework and drag the framework-res.apk file to your desktop
4) Right click the framework-res.apk file and select Open Archive (again, I suggest using 7-zip)
5) Navigate to /res/xml and drag the eri.xml file to your desktop
6) Open the eri.xml file with a hex editor like HxD
7) Press ctrl+f and type Virgin Mobile
8) Highlight the words Virgin Mobile (they appear selected, but highlight them with your mouse)
9) Type what you want, keep it to the same number of characters or less, then type spaces till the rest of Virgin Mobile is gone
10) Save and close the hex editor
11) Drag the eri.xml file back into the framework-res.apk, choose yes to copy, then close the window
12) In the opened ROM archive, navigate to /system/framework and drag your framework-res.apk file into it, then choose yes to copy, and close the window
13) Place the ROM.zip on your sdcard
14) Reboot into recovery, wipe cache, wipe dalvik cache, then install the ROM.zip file as normal
15) Reboot and you should see your customized carrier name on the lock screen and notification dropdown.
[EDIT] Experimental with GSM version of evo 3D, USE AT YOUR OWN RISK.