As for going from v1.46 to v1.7p3 of FOTRS... yeah, it's possible to do so.
Simply deactive everything for it, then clear out the 'MODS' folder, then drop in what's needed to set up for v1.7p3... or simply set up a separate SH4 set up, provided that you have a unmodded virgin copy of SH4 to work with.
As for your career, from v1.46....
" " Version 1.7p3 of Fall of the Rising Sun Ultimate :
Note: This mod is NOT compatible with previous versions of itself. " "
So... Say goodbye to that career saves... Meaning, it's toast.
Now, there is a couple of .cfg files you can keep... But, those are for settings such as graphics, gameplay settings, & main settings... which have no connections to the previous mod version incarnation...
Note : am not at My pc, to list which files out of the save folder to keep, exactly. Sorry... But, know it's at baseline minimum of 2... or 3, that can be kept all the rest... Dump.
propbeanie, s7rikeback, KaleunMarko... can expand on that info...
Hope this info, is helpful...
M.M.