The vowel exchange "a" to "o"

[Petrasti]

Yes, of course there is a vowel exchange in the Romance languages, and this is also the case in German. But as we can see from the Italian examples, the exchange creates words with different meanings in different subject areas, which is also the case in German. In the manuscript, however, we are certainly more limited in terms of subject matter and word usage, especially in the area of plants.
Given the accumulation in a limited environment, I think it is more likely that the words are the same.
And yes, I also think that the a and y are identical for the letter "a", just pronounced as a short and long a. That would increase the interchangeability of a and o many times over. (maybe that's why I noticed it so much) But since this is also a system without ‘proof’, I limited my question to the interchangeability of a in o.