1. No they can’t when referring to the expected pronunciation but if you wrongly use one for another, the risk is low for you not to be understood unless there is a clash with a different actual word. /j/ and /i/ are close but different phonems. In particular, /i/ is a plain vowel that might be stressed and can be pronounced alone while /j/ is a semivowel that can never be stressed and requires an adjacent vowel to be pronounceable. That means that /pje/ is a single syllable word while /pie/ would be a two syllable one, something like pi followed by et.

Here is an example where a mispronunciation would clearly affect understanding:

Quelle belle abbaye ! a.be.i or a.bɛ.i: What a beautiful abbey!

Quelle belle abeille ! a.bɛj: What a beautiful bee!

2. Yuck pronunciation varying, let’s use "yes" as an example. "Yes" starts with a /j/ and is normally a single syllable word while if we force it to start with an /i/, that would be more like spelling the word "es" in English, i.e. the letter E then the letter S. The /j/ sound starting "yes" is used in the remaining French words you cite, not just in fille (/fij/).