Which OpenType feature could I use instead of contextual alternates?

I added a contextual ligature feature to some of my fonts, which uses the Velthuis encoding system.

Some Buddhist scholars use this method for writing Pali as it requires no special fonts to be installed that supports the diacritics. If the contextual alternates feature is applied to Velthuis encoded text in my fonts, it switches to text with the correct diacritics. So, for example: 

Eva.m me sutta.m — eka.m samaya.m Bhagavaa karuusu viharati kammaasadhamma.m naama karuuna.m nigamo

would become:- 

Evaṃ me sutaṃ — ekaṃ samayaṃ Bhagavā kurūsu viharati kammāsadhammaṃ nāma kurūnaṃ nigamo

This is all well and good in PagePlus, where Contextual Ligatures can be disabled or enabled as required.

However, someone recently submitted a "bug report" presumably because they typed an abbreviation like A.D. and were surprised to see it change to AḌ.  I think some applications apply calt by default with no option to disable it!? 

Is there some other feature I could use instead of calt?

My fonts already have Standard Ligatures (liga), discretionary ligatures (dlig), historical ligatures (hlig), Stylistic Alternates (salt) to replace the now obsolete Initial Forms for Decorative Drop Capitals, and Character Variants (cv01) for quick access to symbols.