Can I mark up recommendation letters?

On a signed recommendation letter, can I highlight (e.g. marking up some sentences with yellow color) some points that can support other evidence to make sure Tech Nation reviewers see them?

Thanks.

I wouldn’t. It might give the impression that the letter was edited by you after it was signed by the recommender.

I hear some consultants highlight key words in recommendation and evidence to draw the assessor’s attention

It may not hurt but it doesn’t guarantee assessors will focus on that portion of the evidence