Hello Tim,
Regarding the Point 4, no, xFanatical Foresight does not have the text concatenation action to support full automation. We have the feature in our product backlog, and will introduce them as actions in future versions. We're sorry for the inconvenience for now.
A semi-automated workaround is to use Google Sheet to edit the CSV file, and enter a formula to automate crafting the new email address when you edit the CSV file. For example, given the Original Email Address column as Column A, in the New Email Address column B, enter formula ="s_"&$A2. Click, hold, and drag the bottom right dot of cell B2 and pull down for cell B3, B4..., the formula will prepend text "s_" for all email addresses.
Your feature request is much appreciated for us to improve the product.
Thank you.