Is it possible to have a parameter emptied when I copy a part?
For example: I have a parameter for "Drawing number", and when I copy the part I want this field to be empty so this Drawing number will not be used twice by mistake.
do you mean to copy a part from a random Creo session or is it in the context of an assembly, a drawing?
Are we talking starting a part by copying an existing one? It the latter then it looks like a use case for templates.
If you're talking about taking a part that you have in session, and doing a "Save a Copy As", there isn't any setting or whatnot that I know of to do what you want. If you need to do this sort of thing on a regular basis, you might want to look into developing a mapkey that does the work for you. Admittedly, I'm no mapkey expert, but maybe some folks who are used to making complicated ones can help you. The pseudocode I am thinking of would be something like:
(1) Create a new parameter to store the current part number and copy the part number to that parameter. (2) Blank out the current part number. (3) Do a "Save a Copy As". I don't know how you'll get the file name you want to save under, but I think you can "prompt" for the name. (4) Set the part number back to its original value using the saved parameter from step (1). (5) Delete the "temporary" parameter from step (1).
It's a crude approach, people more conversant in the intricacies of mapkeys will likely find it offensive, but it's a start, I guess.
Myself, I do a lot of copying designs to modify for new things, but I just have a meticulous workflow that makes me set all those unique identifying parameters to "<?>" or something like that. I do them all at the start of the project.