Yes, that's right, but I could add the F-section in the .img file with Gmaptool.
Of course, but ImgTool doesn't have the same prupose as Gmaptool : I wrote Imgtool ( in the beginning for my own utilisation) to make changes in large img files without rewriting or recompiling the file.

Because rewriting or recompiling a large file may be very long (specially when the img file is on an sd card or directly in the memory of the gps unit) and also because it may corrupt the file (after splitting and joining an img file, we are not sure that the new file is identical to the original...) i have tried to write a tool that only changes some bytes in the img file: when you change something in an img file with ImGtool, only the bytes corresponding are changed : no splitting, no joining, no recompiling , so we are sure that all the rest of the file is identical to the original.
For example, when changing the part number, only the 9 bytes are changed (....and the date/time of the file: this last point, because when making a lot of test with the gps unit, I founded out that, if the date/time was unchanged, in the new gmapsupp.img file, the Gps unit often keeps on displaying the old file)
t
But this implies some limitations. For example, if , what Mapsource calls "Nom de l'ensemble de cartes", has 15 characters, ImgTool only allows to change it for a string containing 15 characters or less).

For the moment, only one exception in Imgtool: when adding (not replacing) a typ file in a gmapsupp.img file, in some cases (because , most often, there is a lot of place unused in the FAT after a typ file so the new typ file is written there) , a large part of the img file is rewritten (more precisely, is shifted to make place in the middle of the file)

Maybe, I'll add some new exceptions to increase the functionalities of ImgTool...