Is it legislated to act upon the two hadiths, "keeping the heels together in prostration" and "kneading when leaning on the hand," despite their weak chains of narration as mentioned by Al-Albani? And is acting upon them, while knowing their weakness, considered an innovation (bid'ah)?

Whoever is qualified to examine and weigh evidence must prefer what appears to him to be correct based on the proofs. As for the layman, he must emulate (taqlid (definition)) whomever he trusts among the people of knowledge. There is no harm in emulating Sheikh Al-Albani. The presence of a narrator who has been criticized does not necessarily imply the weakness of the hadith (definition), as there might be something that supports the hadith or authenticates the narrator. No Muslim scholar should be thought to authenticate a hadith while knowing it to be weak.