Solver only allows one range to be entered in the "By changing cells" input field and should be allowed to receive comma separated ranges. This functionality is present in Excel (On both Windows and Mac OS X)
Hi @driveshaftbassist, thanks for reporting. It is by design: https://help.libreoffice.org/scalc/modules/scalc/ui/solverdlg/targetedit?Language=en-US&System=WIN&Version=4.2#bm_id8861964. "The initial variable values are inserted in a rectangular cell range that you enter in the By changing cells box."