This is not specifically what you asked - and i hate to be that guy - however, as a best practice I would create a separate “Routed” report style and call it “Sales Order Ack EMAIL”.
The “Routed” report style is NOT the default - forcing users to explicitly choose the “Email” report style when they want to send out an email version.
Please remember that not all solutions require code.
DaveO
Building on what @DaveOlender and others have alluded to, you can have different report styles but keep the same report. So if you’re concerned about having extra report .RDLs to keep in sync/updated, you can use the same one for both report styles so you still only have to maintain one. I really like Dave’s option and we’ve done this in practice for several reports.
Another place this came up was a solution I was building that involved an email but only if the customer had a certain setting. So if you had a flag that was able to be set using a BPM or similar on the sales order, you could get away with one routed report style and then just use a condition to check the flag in your routing to decide if you want to execute the routing or not. Then you can instruct the users to check the box that says to “do this every time” and click Yes to the routing prompt. Then they won’t be prompted and the logic is still controlled elsewhere.
I was wondering this myself so following the easiest advice above I just created a copy of my main reports i’ve been modifying with routing removed and stuck “NoEmail” into the title then made them default.