The same by what means? I guess you will have to explain the logic in greater detail.
Buttons are created statically in most cases, you simply place a submit-type input in the form, whose action points a view that the action is part of. But I'm not sure there is anything like you described.
I need to change the submit´s action button. I must check in database if already exists a tupla with the same keyword that I want to insert. Understand?
There are a number of ways or approaches in which you can deal with similar problems, for example:
1) You could create your own datatype that would extend the type you're interested in and override its object validation so that in involves checking for older values.
2) You could look for some prepublish hooks/triggers of content views (I believe there may be something like that, although I don't know any for sure).
3) You could create your own module/view that would include such check and otherwise be similar to content/edit. Probably more approaches exists. All depends on how far you're with eZ, usually requires some expertise.