Is Jerk With A Heart Of Jerk a character or plot trope?

Although I generally see it used as a character trope, the description of Jerk with a Heart of Jerk makes it sound a lot like a plot trope, where other members of the cast are given reason to believe a Jerkass has some redeeming trait before finding out she or he really doesn't. Is this a flawed description, or is this actually more of a plot trope than a character trope? (And if so, is it actually mutually exclusive with Jerk with a Heart of Gold after all?)

It can be both a plot and a characterization trope. It states that it's mutually exclusive with Jerk with a Heart of Gold, except for cases where a character may change via Character Development or oscillate from one to the other via Depending on the Writer.

I get that the description says that, but it seems like they could still overlap: a character could both have a plot where their apparent soft spot/justification is revealed to be a facade and still have a legitimate soft spot.

A lot of character tropes can also be described as plot tropes, especially those that require a change in characterisation, or different interpretations or aspects at different times. It's not a problem that a trope can be either.

Jerk with a Heart of Jerk and Jerk with a Heart of Gold are mutually exlusive at the same time, but not for the same character. And that also only goes for being true. You can always play around with tropes and imply them even when they're not actually true.

For instance, you can have a character who's genuinely a Jerk with a Heart of Gold, who puts up a facade of Jerk with a Heart of Jerk whenever another character suspects the first character of being a Jerk with a Heart of Gold.