In the image of your main ROM the keyboard layout should be located at 0DA5H – 0EC4H, 120H Bytes. (Msx Redbook)
The layout is ASCII codes corresponding to the keyboard matrix.

Ex Column 0 Row 0 = ASCII code 30H = Character ‘0’
Column 6 Row 2 = ASCII code 61H = Character ‘a’

With shift pressed:
Ex Column 6 Row 2 = ASCII code 41H = Character ‘A’

Just paste your preferred layout into the ROM and write a new EPROM!!!

TEST in an emulator firsts!

Since you are busy do the following:
002DH Msx Type
00H = Msx 1, 01H = Msx 2.0, 02H = Msx 2+, 03H = Msx TR

002BH Msx ID byte
b0, b1, b2, b3 character generator (0: Japan, 1: United States / International, 2: USSR etc.)
b4, b5, b6 date format (0:Y/M/D, 1:M/D/Y, 2/M/Y)
b7 interrupt period VSYNC (0:60Hz, 1:50Hz)

002CH Msx Keyboard
b0, b1, b2, b3 0: Japan, 1: United States / International, 2: France, 3 UK, 4 Germany, 5 USSR, 6 Spain etc.
b4, b5, b6, b7 information about PRINT USING / Basic version ?

The locations of these tables might not be in the same place for all ROM images. I think you can't be cartain that they are either. You're just lucky if they are.

I know the tables might move, but this is the only info I have. Can anyone give more info etc? The redbook states it works for mainly UK msx's

I would also like more info on the 5 ID bytes 2B, 2C, 2D, 2E, 2F
Country codes etc