Is it permissible to change the intention of shortening the prayer to completing it after commencing it with a traveling congregation, upon remembering that the conditions for shortening do not apply?

If a worshiper changes their intention from shortening the prayer to completing it because it became clear to them that they are not permitted to shorten it, then their prayer is valid and there is nothing upon them. Residence (Iqamah) nullifies the ruling of the concession of shortening the prayer. The default for prayer during travel is to shorten it, and it does not require an intention.