The claim about another artist tampering with the painting supports the further conclusion that restoring the painting is justified, so it can’t be the main conclusion itself.

This correctly characterizes the assertion that another artist tampered with the painting. That assertion is supported by factual evidence, but also supports the main conclusion: the whole reason restoration is justified is because the red wasn’t the original artist’s choice.

The claim about tampering doesn’t clarify any kind of terminology. In fact, no part of the argument focuses on clarifying terminology.

The argument doesn’t state any general position to be defended. The curator’s entire focus is on one specific case, and there’s no general principle stated in the argument.

The claim about tampering is not a restatement, nor is it restated. The curator never repeats a claim, including the true main point that the restoration is justified.