Flying at altitudes below the starting altitude

[Island Xpress]

Here in Tenerife I would sometimes like to fly my Anafi from a rock or a cliff to a level much below the altitude of my starting location.
I see no possibility to create a flight plan as there is no way entering negative altitudes.
Flying manually seems to be possible and while flying the altitude is correctly shown with a minus sign. (Eg. - 11 m)
My question is does anyone know about the limits and/or has own experience?
Can I fly say 250m down and without landing coming back up to my original altitude? Now going up and exceeding the 150m limit? When I would land 250m below, I'm pretty sure Anafi could not come back home.
What if I press the return to home button at an altitude of -200m?
Thanks

 

[Jagerbomb52]

You might want to look this over:
Negative altitude POIs - successful workaround

 

[Island Xpress]

You might want to look this over:
Negative altitude POIs - successful workaround

A very useful link, that most likely solves my problem.
Thank you very much.

 

[Zamzara]

Note that it's only been tested as far as I can see for POIs, while it may work for negative waypoints exercise caution.