It is possible to add expressions involving variables to your templates. For example:
${tool.diameter/2} ${(3.5 + feedrate.cutting)*2} ${2*stepover}
You cannot use string variables such as ${project.partname}, $notes, $totaltime, with the exception of the $CutTime variable, which can be multiplied:
$CutTime*2
Whether your expression is evaluated correctly depends on the template type it's inserted into. For instance, an expression with the {tolerance} variable is only resolved if it's in a toolpath template type or in a summary template type between the <summaryrow> </summaryrow> tags.