Hello Per,
There isn't anyway to make division code 4 not be displayed, the option for a non-displayed division in the CODM requires that you use division code 7. Here is that portion from the CODM user guide:
7. As with other standard divisions, this division may own stops, couplers, tremulants, etc. However, it is different to the other standard divisions in that its objects are not displayed on the standard default console display, due to lack of space.
If your new division is not appearing in the Organ | Keyboards listing, then either you haven't fully updated the proper tables in the CODM file, or perhaps you need to force the ODF to reload and regenerate from the CODM file?
The example 6 all frills example CODM files for St. Anne's uses division code 7 for one of the entries if you want to have a look at that.