How to run nona without any exposure change?

Hello!

I have been using Hugin for years now, but cannot find the right command line switch for the trivial issue:
I have received a pano which is slightly curved, so I want to reproject it just with nona.
The pano is huge, over 48000 pixels wide, so I made an 8192x4096 version to work inside Hugin and find the correct geometric fit.
I have linked the pano image to a grid and optimized to find the 3 values yaw, pitch, rotation. No other corrections are required.

my .pto:
=================================
# hugin project file
#hugin_ptoversion 2
p f2 w6000 h3000 v360 E0 R0 n"PNG"
m g1 i0 f0 m2 p0.00784314
# BTW can anybody explain the p parameter in the m line?

# image lines
#-hugin cropFactor=1
i w8192 h4096 f4 v360 Ra0 Rb0 Rc0 Rd0 Re0 Eev0 Er0 Eb0 r0.174130287671457 p0.38044865440883 y-0.154646062365405 TrX0 TrY0 TrZ0 Tpy0 Tpp0 j0 a0 b0 c0 d0 e0 g0 t0 Va0 Vb0 Vc0 Vd0 Vx0 Vy0 Vm5 n"curvedpano_8192.jpg"
#-hugin cropFactor=1
#i w8192 h4096 f4 v360 Ra0 Rb0 Rc0 Rd0 Re0 Eev0 Er0 Eb0 r0 p0 y0 TrX0 TrY0 TrZ0 Tpy0 Tpp0 j0 a0 b0 c0 d0 e0 g0 t0 Va0 Vb0 Vc0 Vd0 Vx0 Vy0 Vm5 n"grid_8k.png"

# Point links and other lines deleted.
===============================================

The second "grid" image has been disabled after finding the r/p/y values. Also, following some online documentation for the pto file format, I deleted = marks. (Is there a difference or documentation on that?)
Now I tried running nona (additions like -p UINT8 and --ignore-exposure have been my later tries)
"c:\Program Files\Hugin_2018.0\bin\nona.exe" -v -p UINT8 --ignore-exposure straightened.pto -o straightened.png

Remapping and stitching
loading curvedpano_8192.jpg
remapping curvedpano_8192.jpg
blending curvedpano_8192.jpg
saving result straightened.png
Not recognizing known sRGB profile that has been edited

The image is a night sky image, so it's mostly dark, and the resulting image should likewise be mostly dark. I don't want any change in pixel RGB values, just a geometric distortion. Currently some auto-exposure returns a glaringly overexposed and burnt-out image. Whatever sRGB profile is in the file should not change exposure, right? Or how could I get rid of it or fix it? ImageMagick, exiftool, ... ?

As soon as that works, I want to replace the source image by the original, huge panorama. When I tried inside Hugin, I could use it in the preview, but trying to create the new pano crashed immediately. Is that only hugin GUI or is there a known size limit to command-line nona? Would running nona on Ubuntu help? (Windows10-Ubuntu comes with nona 2013.0.0, seems a bit old. I have an older PC with Ubuntu 18.04 but less resources.)

I have searched tens of online manpages and websites. Most docs are from 2007 or so, and further links to somewhere else lead to 404 land. Is there any available up-to-date self-contained documentation that explains every parameter in Hugin 2018.0? I know documenting may be boring, but is important. The p and m lines seem to have new parameters, but are not properly documented.

Kind regards,
Georg Zotti
Stellarium Team