I think what you are asking for could be easily done. However, I think the reason you need it is to be able to map an HL7 field number to a segment offset. There are better ways. It just takes a few more seconds when doing the translation.
Instead of something like:
{IN 0(0).PVI.00133}
in the translate copy. change the 00133 to #3
{IN 0(0).PV1.#3 }
In a translation a field offset number can be used in place of an HL7 field address anywhere. That includes ITERATE statement, IF statements, and all.
It is more self documenting. I don’t think a vendow will ever call to disuss PV1.00133 but he will call to discuss PV1.3. In most cases you have to look up PV1.3 to find out wht it’s HL7 address is and then go look at the translation. Ar eal pain.