There are various occasions in which we have seen managers turn to their sub keeper as an outfield player out of necessity. In others, it has been done for pleasure, as in this Maharlika v Mendiola from the Philippines League, where the visiting team put their substitute goalkeeper on as a striker in added time of the second half.
It happened in the Philippines League. Mendiola, who if they won would secure 4th place and therefore the chance to play in continental competition next season, put their sub keeper on as a striker to waste time in added time of the second half.
Mendiola were winning 2-0 against Maharlika, their opponent for 4th place, and then in the 92nd minute something that isn't often seen happened, at least without needing to.
Mendiola had scored the goal to finish the match (Flores in the 90th), and their manager made the last change in added time. An outfield player came off for their sub keeper.