Assuming you are using windchill with Creo;
Select "continue" instead of "read only". The model will be modified but will not be checked out and will not cause problems when checking in your assembly ( im not sure if there are additional winchill settings for this).
By the way if Creo want to regenerate a model, there is usually something not good with that model, better to check out, regenerate and read the message area.
