I am using a precompiled preamble with the \documentclass inside. However, I sometimes want to change the document to 'draftmode'. Recompile the preamble everytime I am doing this is not so comfortable. So it is somehow possible to activate the draftmode even after the command \documentclass in the preamble?
The full definition of the
draft option in the standard classes is
so you can get the equivalent effect by doing
at any point.
[draft] on document class makes it a global option so it may have had an effect on packages you have loaded (but you have not given any information on which packages).
Most packages will ignore it, some may just set a flag to true for draft mode, in which case you may be able to set that flag to false, but some packages may alter the code loading and so not load the "normal" code at all in draft mode. The behaviour is all specific to each packages handling of any
draft option that it has.