With HRP v5.2 or later, it is actually possible to use the older Polymost renderer without suffering issues, e.g. badly aligned HUD weapons. Here is what you need to do:
Create a shortcut to eduke32.exe (if you have not done so already). To do it, right-click
on eduke32.exe in your Duke3D directory, choose "Send to" and "Desktop (Create shortcut)".
Edit the shortcut by right-clicking it on the desktop and choose "Properties".
The "Shortcut" tab will be opened directly. There, you have to add the parameter
-hduke3d_hrp_polymost.def to the "Target" command line. Click on "Apply" to confirm your changes.
When launching EDuke32 via the shortcut, a launcher will pop up. There, be sure to deactivate
(i.e. untick) the Polymer renderer option. You should now be ready to enjoy the HRP with Polymost!
If you are running other mods like DukePlus at the same time, you will still run into trouble with Polymost since those mods
usually bring different def files with them, overriding any HRP definitions. Please use the Polymost HRP Override Pack provided by LeoD to avoid this issue.