All works as expected except i cannot edit the row template of the copied/cloned data grid when doing this to another stack..
*snip*
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EDIT: i solved the issue by not cloning new data grid template stack to the destination topstack, but instead copying the card corresponding to the source data grid to the destination data grid's template substack (creating a new substack from scratch if needed first).
The end result is that this can now
- copy an existing substack to a new stack and i will work as expected
- 'clone' a stack so that the destination stack is identical to the source stack even if on another stack
On my testing both methods should produce a faithful replica of the source datagrid and now the row template can be edited normally.
Would be really grateful if others could test -- make sure you're not using this on critical work when testing though (i take no responsibility

Many thanks
Stam
--- EDIT ---
Attachment removed as several bugs were found. New post for fixed version below.