Answer: The Gemara (Yoma 70a) writes that while one should not normally read pesukim from the Torah off by heart, the kohen gadol would do so, so as not to cause tircha detzibbura, an unnecessary burden on the community while they would roll the sefer torah (See Mishna Berura 49:3).
Accordingly, Rambam (Tefilla 12:23) and the Shulchan Aruch (OC 144:3) write that one shouldn’t roll a sefer Torah during kerias hatorah. Thus, when we read the maftir from a different sidra, we should remove another sefer Torah when possible.
R’ Ovadia Yosef (Yabia Omer 8:15:4) quotes many poskim who forbid returning a sefer Torah to the aron hakodesh once it has been taken out. As people may erroneously think that this sefer Torah isn’t kosher, it is deemed to be disrespectful to the sefer Torah (See Kitzur Shulchan Aruch 78:10).
The Kaf Hachaim (OC 144:13) and R’ Moshe Feinstein (Igros Moshe OC 2:37) write that there is a machlokes as to whether one may return a sefer Torah that is rolled to the wrong place as on the one hand we are concerned for the kavod of the sefer Torah, while on the other hand we don’t want to cause tircha detzibbura. The Kaf Hachaim concludes that one mustn’t return the sefer Torah. R’ Moshe, however, writes that the community can choose whether to roll the sefer Torah or to return it to the aron hakodesh.
In conclusion, while the sefardi poskim write that one should roll the sefer Torah, ashkenazim would be able to replace it and exchange it for one rolled to the right place if necessary.