This would depend on the design of your process. If you are using the out-of-the-box "Get Email Content" operator, the results of this operator are in a variable called something like this:
Process.Get_Email_Content_1.MessageContent
You should be able to manipulate that variable after this operator has run to add/remove data from it before passing that to Service Desk.
If you are using the "Send Mail" operator to send the data to Service Desk, you can put variables into the properties of that operator to be the edited content from the "Get Email Content" operator. This shouldn't change anything with attachments.