Remember that LorentzIndex[mu, 4] is simplified to LorentzIndex[mu] and Momentum[p, 4] to Momentum[p]. Thus the fullowing objects are defined in four dimensions.
This changes all non-4-dimensional objects to 4-dimensional ones.
Consider the following list of 4- and D-dimensional object.
Any explicit occurence of D (like in f(D)) is not replaced by ChangeDimension.
The option Dimension of Eps must be changed too, since with the default setting Dimension
4 the arguments of Eps are automatically changed to 4 dimensions.