I tried following the answer in TeXForm and Symobilze, however, I have trouble making it work. I loaded the Notation packages and symbolized all expressions with a subscript as in the example. I defined the same test function using Ctrl+_, I do obtain the same output for TeXForm and FullForm before loading updateSubscriptTraditionalForm. However, after loading it, TeXForm still gives me the same output?
After some more experimentation, it would seem that using StandardForm inside TeXForm works, all the while keeping the WorkingForm default:
Needs["Notation`"]; Symbolize[ParsedBoxWrapper[SubscriptBox["_", "_"]]] TeXForm[StandardForm[Subscript[a, 1]]]
Instead of just
TeXForm[Subscript[a, 1]]. I am not sure why/how, but it works.