  Synthesis consists in deciding whether a given labeled transition system (TS)
$A$ can be implemented by a net $N$ of type $\tau$. In case of a negative
decision, it may be possible to convert $A$ into an implementable TS $B$ by
applying various modification techniques, like relabeling edges that previously
had the same label, suppressing edges/states/events, etc. It may however be
useful to limit the number of such modifications to stay close to the original
problem, or optimize the technique. In this paper, we show that most of the
corresponding problems are NP-complete if $\tau$ corresponds to the type of
flip-flop nets or some flip-flop net derivatives.
