Installing KDE in Gentoo
 

Not a newbie in Linux, only Gentoo. :)

I was installing kde when I found out I didn't have the ql in my USE variable. I rebooted the system, added it and emerged kde again. Will this affect anything?

What is ql? I've never heard of this use flag.

did you mean qt?

Yes.

It will not affect anything. Re-emerging will merely compile KDE again (if you can stand the compile times) and everything will be fresh and ready to go.

In fact, updates are also done using the same emerge command as the one used to install.

For example if you used to install program ABC:

emerge ABC

To update ABC also, you use the same command. Nothing shoud break.