I find the answer (ROOT: roofit/roofitcore/inc/RooGlobalFunc.h Source File)
inline RooCmdArg Offset(bool flag=true) { return flag ? Offset("initial") : Offset("off"); }
According to the code, Offset(true) is equal to Offset("initial"). So, at a glance, we cannot set Offset("bin"), in RooMinimizer and ProfileLikelihoodTestStat. Is there any way to do this?