HALion has a full set of General Midi instruments which play over the complete 10 octave MIDI keyboard range, though obviously they don’t sound realistic for notes that are a long way outside the real range of the instrument.
Somebody posted a thread saying it was possible to set up HALion to use the “high quality” instruments and extend the range with a GM instrument. I haven’t actually tried that yet, but I have the basic same requirement as you - for example 17th/18th century French horn parts sometimes go higher than the “standard” range of modern orchestral horns.
The functionality to control a different sample library is quite limited in the current version (different vendor’s libraries tend to do things in different ways), so I think it’s worth waiting for the next update before getting too deep into this. Just loading patches with names including “GM” into HALION will get you the extra notes for minimum effort right now, if you don’t mind lower quality sounds.
If you want “genuine” playback of obsolete instruments, that probably means searching out specialist sample libraries. On the other hand some libraries (but AFAIK not the “lite” version of HALion that comes with Dorico) let you tweak the way the samples are mapped onto notes yourself, so you can extend the range of an instrument. That is quite easy to do with the Garritan libraries for example, because the instrument definitions are stored in plain text files that you can edit. Some other libraries (including HALion) use proprietary file formats and you need special editing software that comes with the library.