tstToString[expr_?(FixedPointList[Head,#][[-3]]===bla&)]:=ToString[expr];

tstToString2[expr_?(head[#]===bla&)]:=ToString[expr];

head[expr_]:=FixedPointList[Head,expr][[-3]]

ParallelDo[Print[tstToString[bla[{f, pe, 0}][1][1, 0]]<>"b"],{vv,0,0}]