Following a brief "moment" of (unjustified) doubt (but justified requirement to verify), it now seems the "re-wrap work-around" does work, and HDLink does re-wrap provided its "Force Re-Wrap" option is enabled in Cineform's HDLink (otherwise it re-encodes to 8-bits).
My only issues were niggling ones with HDLink, in terms of the mentioned setting-requirement and also its (repeatable) crash/freeze issue at the end of processing, requiring a process-abort (from Windows' Task Manager). Fortunately this ugly state of affairs does not appear to harm the generated AVI file, other than to fail to update Windows Explorer and also the file's Accessed/Modified timestamps at the end of processing.
In practice, the AVI file generated from this process was found to be playable by Windows Media Player and importable by Premiere CS6, where it appeared as expected in both 8-bit and "max bits" modes, the latter receiving the full 10 bits of levels information.
So problem solved! Verified!
Just for the record, the "moment of doubt" and the resolution of it:
Oops... need to verify, properly this time, whether that workaround actually worked...
Following an overnight conversion, the result seemed to be only 8-bits. This view was supported by file-size reduction (39GB to 31GB, proportion = 8/10) and by 8-bit-like levels-banding when viewed on Premiere's Waveform/YC Monitor on a Premiere CS6 test Sequence in Max Bits mode.
...In which case my quick test previously suggesting that re-wrapping had fixed the problem was in fact misleading, because it was not only changing the container (QT->AVI) but also the encoding and the bit depth... So the result of that test was neutral...
So now I will re-try HDLink conversion, but this time with HDLink's "Force Re-Wrap" option selected in its Preferences.
<Some time passes...>
This time, it took only 45 minutes to complete and furthermore the CPU (4-core) load was tiny, just 1 or 2%, as opposed to around 16% for the overnight "unwanted re-encode" process. Both of those factors are supportive of the prospect that re-wrapping was indeed happening this time...
Then HDLink failed to terminate properly. After 30 further minutes, there was no change, and no CPU load from it, so I elected to abort its process.
The resulting AVI file was of almost exactly the same size as the QT original, was interpreted correctly when Premiere was in "Max Bits Mode" and verified as containing a useful 10 bits of information (via banding in Premiere Waveform/YC Monitor, comparing with and without "Max Bits Mode") .
This "Video Detective" can now hopefully say "Case Closed", but I'll "leave the files open" for a few days more in case any further issues show up.
Regardless, it would still be helpful to hear of anyone with similar experiences or alternative solutions.