The attainable accuracy of the X 2 Σ(v,N)=(0,0)→(vu,0) transition frequencies of optically trapped 174Yb6Li molecules are analyzed (vu=1,2,3,4) to test the variation in the proton-to-electron mass ratio. We eliminate the Stark shifts induced by the trap and Raman lasers by choosing appropriate frequencies (magic frequencies). For vu=1 and 2, we obtain more than one experimentally useful magic frequency, thereby leading to more choice in the trap laser. For vu=3 and 4, the choice in the trap laser is limited. The systematic frequency uncertainty is given by the trap laser frequency detuning from the magic frequency and the fluctuation of the power ratio of the two Raman lasers and can be lower than 10−16 for all these transition frequencies. To obtain lower statistical uncertainty, measurement with vu=4 is more advantageous than that with vu=1−3.