Is feigning prayer without ablution to avoid being accused by others of hypocrisy considered apostasy, and does repentance erase the sin of this act?

All praise is due to Allah for guiding you to repent from the sin of abandoning prayer and feigning it without ablution. Abandoning prayer is one of the gravest sins, indeed it is considered disbelief by many scholars. As for feigning prayer without ablution, it is a major sin but does not reach the level of major disbelief. Your repentance, Allah willing, erases the effect of the sin. However, you must make up the prayers you missed or performed without ablution, according to the majority of scholars, because they are a debt upon you.