For the engagement letter, you would be manually revising the text. There is, however, a place where you can specify the framework and you might find this useful. You can delete/turn off text and paragraphs that are not applicable.
You might also find it easier to create your own letter using one of our blank additional letters available in GENMST. These already have headers, footers, signature block, and salutations built in along with empty paragraphs where you can free-form type in your content (similar to the engagement report).
