Sorry for any ambiguity, but I don't think cost/resolving plays a role in this. The scenario at hand isn't one where the effect fizzles for losing its target before it can resolve; the question is wether not an already tapped/untapped card is an eligible target for an effect that taps/untaps its target as part of the resolving-process to begin with (as stated above, could one use Tamiyo's effect on a tapped card, or Scryb Ranger on an untapped one just for the sake of paying their respective costs?)

Thanks for the immediate response, but I'm not entirely sure if that covers the question - as stated above, all effects that use (un)tapping as a cost beyond the respective symbols already specify that only un/tapped permanents are eligible. My question was whether not there is any rule preventing me from, for example, targetting an already tapped permanent with a targetted tap-effect. EDIT: Ah alright, thanks for the clarification.