Company lawyers says I can get a new job with the same employer without waiting 180 days (concurrent filing)

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Hi, I'll soon be filing i140-i485 concurrently for a EB2-ROW (currently in 6th H1B year). Company lawyers say I can get a new job within the same company right after the i140 is approved (using premium processing) and there is not need to wait 180 days of i485 being pending (AC21) if the job is in the same or similar category.  They haven't explain how they will do this.

1) the only way I see this done is if they file a 1-yr H1B extension with the i140 to the new role and then start the whole process again (PERM/i140)? Is this doable? And is there a way to do this and avoid having to go through the PERM/i140 again (adding 1.5yrs to be in the same spot again)?

2) Is there any other way that would allow me to retain my i140 and PD (without having to go back to my current position once i485 is approved)?