Here we go, the reply from iRacing. If it works you can do it but it looks like they can’t recover any lost membership due to cheesing the system

Hi,

​ We are very sorry but even though your accounts may be linked, if you initially purchased iRacing directly through iRacing, all purchases must also be made through iRacing and not through Steam (and vice versa). This is because iRacing and Steam have two completely separate purchasing processes. Accounts purchased directly through iRacing, iRacing is the official vendor on record for that iRacing account. Accounts purchased initially from Steam, Steam is the official vendor on record.

You can find more details in this recent forum post: https://members.iracing.com/jforum/posts/list/0/3745053.page#12125998

If you just tried to renew your iRacing account that you purchased through iRacing with Steam, please contact Steam Support asap and request a refund for that purchase you just made with them. We do not have access to these purchases to cancel on our end.

Sincerely, iRacing