If you have already created an OS image and you have to modify-build-download it several times you can use a shortcut to perform those operations as fast as it is possible (if you do not add new components – which implies a sysgen): you can modify reginit.ini (for registry entries) and ce.bib (for files/modules to include in the OS image) then run from the command prompt:
regcomp %_FLATRELEASEDIR%\reginit.ini %_FLATRELEASEDIR%
romimage %_FLATRELEASEDIR%\ce.bib
The first command compresses the reginit.ini file to create some files which are included in the image in ce.bib:
If your OS image includes the hive-based registry the files are:
- boot.hv
- default.hv
- user.hv
If your OS image includes the RAM-based registry the files are:
- default.fdf
The second step processes ce.bib to create the new OS image. You can create a batch file which run the two commands and put it in your DEVELOPR (*) folder.
Be careful: everytime you run makeimg all your changes will be lost since reginit.ini and ce.bib will be rebuilt.
(*) If you create a %_WINCEROOT%\DEVELOPR\%USERNAME% directory, this will be in the path when you open a command prompt from Platform Builder. More info on this on this Bruce Eitman’s blog post.
Windows Embedded Annotations 
Very useful, I made WINCE image in less then 3 minutes, instead of more than an hour!
TY.
Glad to help. Be careful though: everytime you run makeimg all your changes will be lost since reginit.ini and ce.bib will be rebuilt so you may lost your modifications.