Good day.
if I have a shape that needs to be cut out for example the width is 30mm.
After cutting and testing the part wont fit and I need to make it 31mm width...what would be the best way to tackle this? in Mach 4 without having to redraw again and import.

attached and pic of the example the red cross to be cut out and the yellow to be done after the item wont fit.

Thank you!

You can use Cutter Compensation to achieve this. 
Page 76 and Page 77 of the Mill G Code Programming Manual will tell you how to do this. 
When you call up your tool, you can activate cutter comp with either G41 or G42.  If you are climb milling then use G41, if you are conventional milling then use G42 since you are profiling the outside of this cross it looks like.  See Page 77 for more details.  The manual is located in the Mach4 Folder and then in the Docs folder.
Put the G41/G42 on the first line of your G1 feed move; this will activate cutter comp.  Once you finish the profile, use a G40 to cancel the cutter compensation.
You will notice in the manual that there are two ways to apply a specific amount of cutter compensation; using D or P.  Using D, you will use the tool number you are using to machine this part; Example:  D5 if you are using tool 5.  You will have to put the tool diameter in the "Diameter"   section of the tool table.  If you want to cut more, then you will make the tool diameter smaller in the tool table. Example:  0.125" endmill --> make it 0.123" to cut more. 
Using P, you will just put tool diameter with the desired adjustment.  Example:  G41 P 0.123" G01 X## Y##

Man I could not make it to work.
In the end I installed vectric on the control pc and make adjustment as need and reload gcode.

Thanks!