I realize the post I'm replying to is 6 years old. In fact, while Googling for a solution to this problem, I found a post from 1999 talking about the same issue. Yet, in 2012, in persists. Incredible that Autodesk has not fixed this major bug in its STB implementation at some point in the past 13 years...
In any case, a quick (if imperfect) workaround I found to the problem is:
1. Use CONVERTCTB to create a new STB from a CTB that you have. This creates an STB with a color mapping table. Change the style names to suit your desire. However, once you do so, the file becomes corrupted and whenever you open it, it comes up with an "invalid style name" error. This doesn't keep the file from being used, but it does give you this error whenever it is opened or a drawing uses it. You also cannot add new styles to the STB. Thus, do not use this as your primary plot style. Only use it as a style for converting drawings from CTB to STB.
2. Use CONVERTCTB to create a new STB from the same CTB as before. This time, go to the "General" tab and click the button that says "Delete R14 Color Mapping Table". It comes up with a dialog box. Press OK. Now rename all your styles to the same names as in first converted STB, above. If you close or open this file, or use it for drawings, it does not become corrupted. However, since it no longer has a color mapping table, you cannot convert drawings with it. Thus, you need both files.
You can use the first STB to convert a drawing and then change that drawing's plot style in the plot dialog box to the second STB, so it won't give you the "invalid style name" error when you're in the drawing. The list of styles existing drawings can be mapped to will always be limited to the list in the first file, but you can add styles to the second one, thus allowing more versatility when adding geometry to old drawings or using it for new drawings.
Thanks LM. The problem I encountered is that the renamed styles cannot have spaces (not sure about special characters). We are trying to switch from our CTB to NCS STB, e.g. "Extra Wide" etc. Unfortunatly we'll have to make the style name Extra_Wide, for our CTB to STB conversion file. Then when NCS STB file is applied it won't map to the correct style, i.e. we'll get a (missing) style error.
Anybody come across this and have a good solution?