Hi, Sage,  Rich,  Mark & All
As Mark stated it, It will work fine.
But it won't allow you to use G90, G91.1 or G9...'s on the same line in the Initialization String, only re-sets the G91.1.
Not trying to complicated setting in Mach3 for New User's Hear,!!!
Hears a Macro to use in the Ini-String Line, I think it will Re-Set Most Situations that we can get into with G-code. 
' ( M1111.M1S Macro )
' ( Needs to be installed in C:\Mach3\Macros\Mach3Mill Folder)
' ( Basic Default Location or as needed )
' ( Change it as your need )
' ( For MM Units Replace G20 with G21 )
' ( For CV Mode Replace G61 with G64 )
Code "G17" '            Set X,Y Plane
Code "G20" '            Set INCH Units Mode, MM "G21"
Code "G40" '            Cancle Cutter Radius Comp.  
Code "G49" '            Cancle Tool Length Offset
Code "G50" '            Re-Set All Scale Factors To 1.0
Code "G61" '            Set Exact Stop Mode, CV "G64"
Code "G69" '            Cancel G68 Rotate Coordinate System 
Code "G80" '            Cancle Canned Cycle Mode 
Code "G90" '            Set ABS Mode
Code "G91.1" '          Set IJ's INC Mode
Code "G94" '            Set Feed Per Minute Mode
Code "G52 x0 y0 z0" '   Re-Set Temp Offset Mode
Code "F10" '            Set Default F Speed To 10
Code "M30" '            Program End and Rewind G-Code
Just a Beginner, Compared to So-So Many Great People Hear.
Chip
Edit: Changed the Execution Order a bit, Tested it some more, Using ver 3.042.015,  Let Me Know what you find.