I am always happy to have as many singers singing my songs as possible, and so, I am fine with transpositions, as long as the accompaniment can also work in the new key. Some adjustments might be necessary: for example, a section may sound great on piano in the original key but transposed down a third, it might sound muddy. When the song has an accompaniment other than piano, similar difficulties might arise. Generally, these problems can be solved and I am delighted to assist.
In some instances (see “Living in the Body”), I have provided guidelines for conversion to a different voice type. And sometimes, after many years, I will make a new official version (i.e., the mezzo-soprano version of I Never Saw Another Butterfly.)