Hi!
If you convert your game key to steam, is it possible to go back to the stand-alone launcher afterwards, or are you then locked to using Steam?
And for those among us with several game keys (ex. Gold Supporters), I guess converting one key will not affect the others, correct?
I was just about to say, “how does that affect you?”, you can convert your key(s) but there’s no way back, no. In your case you can convert one and leave the others. 
OK, thanks for clarifying
Killrob, one more question regarding the topic. Is it necessary for me to create a seperate forum account, or can I play on my current account with one key converted to Steam, and one unconverted for use in the original launcher?
Your forum account is unaffected, so you can just choose to convert one key to Steam and use it independently. Your Steam Automation account is linked to your Steam account name. So you can have both without issues.
Great