Record Producer: Keep previous MRVS rows when dropdown changes, and add new rows as extra columns (o

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Service Catalog → Record Producer → MRVS (Multi‑Row Variable Set)

Release:
(please add your release, e.g., Vancouver/Washington)

What I’m trying to do
On a Record Producer, I have a dropdown (select box). Based on the selected option, I populate a Multi‑Row Variable Set (MRVS) using an onChange Client Script.
My requirement is:

1. When the user changes the dropdown again, the previously inserted MRVS data must remain, and
2. The new selection should append additional data:
   • Option A: Add the new data as additional columns to the same MRVS (if possible)
   • Option B: If columns can’t be created dynamically, then show one more MRVS and keep all MRVS rows together in the same request submission

Finally, submit everything in a single request.

What I already do

• I populate the MRVS rows on dropdown onChange using client script (g_form) with JSON.
• The MRVS repopulates correctly for the current selection, but when selection changes, previous rows are lost.
• I’m looking for a clean pattern to merge previous rows with new rows and guidance on columns vs extra MRVS.

Questions

1. What is the recommended pattern to retain previous MRVS rows and append rows for the new selection?
2. Can MRVS columns be added dynamically at runtime? If not, what is the best design (single MRVS with superset columns + conditional show/hide, or multiple MRVS)?
3. Best practice to merge MRVS JSON values on client side (without server round‑trip) and to load option‑specific rows via GlideAjax when needed?
4. Any caveats for UI Policies / Catalog Client Scripts with MRVS JSON?