I have developed the function for Shifting the longitudes in maps. You can find it here: https://earth.bsc.es/gitlab/es/ClimProjDiags/-/blob/develop-ShiftLon/R/ShiftLon.R
It has basic documentation and an example (you can find an example a bit more complex in issue #9 (closed)). Could you please take a look at it and let me know if you want me to add/remove/modify anything?
Thank you!
Carlos