Hi Martin,
It sounds like you are wanting to make custom profiling targets, esp. for scanners, and therefore need to be able to measure the targets and get accurate reference information. What you are calling a description file is usually referred to as a “reference” file. This is the file that the measurement file is compared to in order to create a profile.
If you have a dongle-version of MeasureTool, it has a Testchart Generator that you can use to easily create custom profiling targets of any size for a number of different spectrophotometers. Colorport by Xrite will also allow you to create profiling targets. X-Rite also has a sort of “in house” software that is not supported called Colorlab which does many of these same functions. All of this software is available from X-Rite. Colorport and Colorlab are free. All of these will generate a reference file without you having to manually edit text files.
Also a spreadsheet program is very handy here. Excel can allow you to copy and paste whole rows or columns, and fill in columns using the same numbering pattern. Excel can import and export in text format also.
Once you have a printed target image, you would of course have to measure the patches in order to create the reference file which you would then use with the scanned image of your target to make a scanner profile. So, keep in mind your ability to read the patches when you layout your target (patch size, etc.)
Keep in mind that this printed target would be limited to the gamut of your printer - not necessarily well represented of the gamut of your scanner. Scanner profiling software generally tends to go beyond the limits of the measured target in creating a scanner profile. It sort of makes some educated guesses as to the more saturated portions of the profile, so that the profile will have some idea of what to do with colors that are outside of the gamut of the profiling target.