Add workflow "pre-function"

Please would it be possible to add "pre-function" to the workflow engine?

It would help in some cases that are not possible to do now or in very complicated way.

The main purpose is here:

1) defautl value created in workflow not in custom field

To create default value make much more sense in workflow action (before or after the screen is shown to user).

It makes sense for example for custom field "division", when we put some default value for each user and for each issue type diffrent. Then this is shown to user and the user still has the possibility to change it. 

This cannot be done in post-functions.

2) delete the field value before the user can put the own value.

3) you can add the logic here because you could use functions simmilar like in post-functions. So you can do nerly every conditions before you put some values to the fields.

Best Regards