cschnell

Perhaps my wording was wrong.
I am trying to change which data source a single report is linking to. Inside the repository, editing the JRXML report, on the page called Link a Data Source to the Report, I have changed the data source (created as you mentioned) from the repository to my development data source and saved.
(similar to this page https://community.jaspersoft.com/documentation/jasperreports-server-user-guide/defining-data-source )
While investigating this, however, I found that my input parameter was linked to the production data source. This is why the report didn't appear to be changing. I thought I had it linked to no data source. Once I changed it, it is now working properly.
When I run the report, it still shows data from the previous data source.

While I thought I had my parameters mapped, apparently you also need to have the below parameter in the "Parameters Map" expression.
$P{REPORT_PARAMETERS_MAP}
After I added this, it worked.

It looks like my comment about using raw SQL in the parameter was key.  I reread the article I linked and looked for more specfic articles and found it was as simple as putting "@rn1 := if(@pk1=A.order_id, @rn1+1,1) as rowNumber," into the Default Expression of my parameter rn1 and using $P!{rn1} in its place. 
I kind of wish the documentation on this was a little clearer, but it worked.

An update and so slightly different question: I managed to get this to work properly in the preview in Jaspersoft Studio.  All fields wrap and flow onto the second page with no gap between Group 1 Header and Group 1 footer.  I'm not 100% sure what I did that caused it other than the last thing I remember doing was changing all frames to No Stretch.  All text fields have Stretch with Overflow with type relative to tallest object.  For the group, I have Keep together selected and split type to stretch. 
I have both Jaspersoft Studio and Server running on 6.4.3.  When I preview the above in Studio it's perfect, only two pages long.  When I run it on the server, it's three pages with 90% of page 2 blank other than what flowed over from page 1 (group header).  Page 3 is all of the group footer.  I tried previewing in different formats, the same as I export to on the server and the results are the same, perfect on studio and wrong on the server. 
I must be missing a setting on the server, but for the life of me, I don't know what.  Anyone have any hints?
 
In addition to the above, I found that the Group Header/Footers could be no more than 600px (on a normal Letter size page).  Once I separated the groups more making them less than 600px, the groups then flowed together in both preview and on the server.