If you are able to type Unicodes you get proper glyphs in InDesign and FireFox (these two I checked just now).
Back to the font:
In FontLab Studio:
edit file c:\Program Files\Common Files\Data\uranges.dat :
0x10A00,0x10A5F,10A00 Kharoshthi # after this line
0x11100,0x1114F,11100 Chakma # add a line with desired Unicode range
0x12000,0x123FF,12000 Cuneiform # the rest of the file
Open FLS, choose "Chakma" Unicode range and add glyphs into their proper slots.
In TypeTool (probably) you need to open the font which contains Chakma range and add glyphs into their proper slots.
You can download installable FontForge for windows from:
http://sourceforge.net/projects/fontforge/ .
FontForge is free (BSD licence), info
http://fontforge.org/. Is a bit challenging and not rock steady.
regards
PS feel free PM me if you need more info.