I use the Nusach Sefard. I have collected various siddurim with Sefard and have noticed a change in the Shemoneh Esrei a long with other stuff. I understand you can’t switch nusachim when you established one for yourself, but what about changing siddurim with variations of the same nusach? If you look at ArtScroll, then Koren, then others, you’ll find variations. I’m asking especially for nusach Sefard, not Ari. Thanks.
Shalom, Thank you for your question. The question of different versions of prayer, according to custom and community is an interesting one. Traditionally, a person was bought up in a perticular place, and part of a long chain of tradition associated with that place and their family. So, the Jews of a certain place pretty much prayed according to a certain siddur – the Morrocans with their siddur and those from Hungary with theirs. Of course people moved, and also changes and new versions were introduced in certain periods (such as the Chasidic movement's changes in prayers). But, by in large one siddur was used for generations. For your correspondence it sounds as though you were not bought up with a particular nusach or siddur, but rather “established one for yourself”. That being the case, you should try to stick to that nusach – however, you probably did not intend to particularly choose version A over version B (and you may not even have been aware that there are subtle differences within the nusach Sefard). That being so, feel free to find the particular wording of your Nusach that you feel best with. On the whole that should be in line with the community you are a part of, if they have a set siddur, it would be advisable to use it. But, if you do not feel part of any one community, you may choose for yourself which siddur to pray from. Blessings.