I have variables in an expression that have been previously expanded into their real and imaginary parts, that I later wish to recombine to a single variable. For example, a function or operation that would be able to convert $\sqrt{2} \,\textrm{Re}(a) - i \sqrt{2} \,\textrm{Im}(a)$ back to $\sqrt{2} \,a^*$, etc.
Is there a function I am missing that already does this? FullSimplify
does achieve this, but also converts the $\sqrt{2}$ into a decimal and takes a lot of time for longer expressions, which is not ideal.