lol there are detailed guides on this you should read them
assuming you have d2loader
1. download onlyer's d2 cdkey refiller
2. copy cdkey.mpq to your diablo II directory
3. edit autocdkey.reg, enter your second classic & LoD CD-keys
4. run autocdkey.reg
5. run d2cdkey.exe and click refill both CD keys
6. run makecdkeyhash.exe, click enter CD key manually
7. enter second classic CD key
8. copy hash to clipboard
9. run makecdkeyfile.exe, make a keyfile name it something NOT d2jsp.key
10. edit the keyfile, copy the long line of code
11. delete the keyfile
12. edit d2jsp.key, add the copied long line of code under the original long line of code in d2jsp.key so you got 2 key hashes in that file
13. set up your first settign in autod2jsp.exe normally
14. set up the setting you want to use on your other account in autod2jsp.exe normally but also check "use cdkey.mpq"
15. run both, if the second one gives you error "0" or unknown game version you messed up steps 6-12
16. if it gives you error 998, rename your plugin folder
17. if it lags too much use low quality no sound and 640xsomething and keep them both minimized
easy