Can you change the label and caption for an OOTB object in Clarity?
For example, to change all labels and captions of the 'Incident' or 'Idea' object, in the user interface to a custom name?
That is, replace an OOTB Object with a Custom Object?
No. There is no easy way to change the name of an Object so that it flows throughout the whole CA PPM interface.
With Menu Manager you can you change the Object name on Menus so that it appears as something different easily enough.
Once you are onto that Object's page though, the trail at the top will still reference the Object name, and potentially confuse the user.
It can't be done with UI themes either.
While, it may be possible to completely duplicate and rebuild a custom Object, it is seldom a good use of resources.
And with every upgrade, the question will need to be asked about whether new fields need mapping.
Training to use the new terminology is the recommended path.
For a good Community user comment on why adapting to the product is often a better process than customizing at this level, see here:
Custom object to replace OOTB Idea object - not advisable?