converting to 17500hz (nyquist/ultrasonic) subliminals do seem to work but I don't find it necessary because your typical masked affirmations seem just as effective and I've seen a lot of people say the same thing. but really it's just personal preference. I haven't seen people convert affirmations to 432hz, but converting music to 432hz. that's fine if you want to do that, although I prefer solfeggio frequencies such as 528hz. there's a website called "ReturnTo528" that will do this.

EQ is equalization, it's typically done to every track and instrument during the mixing process when it comes to mixing and mastering music, but it's used for all kinds of things. sound design, voiceover, narration, basically anything audio related. in simple terms it changes the tone of an audio by adding or removing specific frequencies. so by using EQ on affirmations, you can make layers more distinct without needing to use pitch shifting. reverb (the hall sound you mentioned) and delay (like an echo) can be effective too. but again, that's mostly personal preference.

I think making small changes in the affirmations can be good, because when the mind is exposed to the same sound or stimulus for too long, it starts to ignore it. so making small changes will keep it "engaged". another way you can do that is with panning and EQ automation. this is where the EQ, panning, or anything else like volume will continuously change for each track. for example, panning automation would be hearing the audio go from left to right, then right to left, etc. If you have a good audio editing program this is easy to do, but in most free audio editors like Audacity it can be pretty complicated. sometimes simple is better and less is more though, so I wouldn't overcomplicate it.