Thanks for confirming @Subramanyam . The other thing that you confirmed also is the order of the columns in the merge.
However, I believe you meant this:
20030856912022070120220508PGT
instead of this:
20030856910701202220220508PGT
Is that correct? (you mentioned that the merge is done after the format change)
So, for #1, the format change, you can use this expression via the String Manipulation: join(substr($Docum$, 4), substr($Docum$, 0, 2), substr($Docum$, 2, 2))
This will change:
07012022
To this:
20220701
But you can do both #1 and #2 in the same expression, like this: