I'm not familiar with "kiwiirc.com" - I gather that is some sort of web-based interface to iRC? I have always used standalone IRC clients (eg, XChat) and they always provide option to remember your preferred channels and nicknames.
When I use IRC to access #musescore, do the following.
1) click the link.
<a href="https://kiwiirc.com/client/irc.freenode.net/?nick=musescore|?#musescore" target="_blank">https://kiwiirc.com/client/irc.freenode.net/?nick=musescore|?#musescore
2) login as whatever default it offers me. E.g., musescore|17667
3) from inside IRC, change my nickname from musescore|17667 to jim-newton
Is there an easier way? Can I "create" a login called jim-newton with a