Are the old A-head terminals for connecting to knob and tube wiring still compliant?
The article you need to refer to is 394.
Here is an excerpt that applies to your situation.

II. Installation
394.10 Uses Permitted. Concealed knob-and-tube wiring shall be permitted to be installed in the hollow spaces of walls and ceilings, or in unfinished attics and roof spaces as provided by 394.23, only as follows:
(1) For extensions of existing installations
(2) Elsewhere by special permission

Many jurisdictions don't allow K &amp; T unless it is a historical house. For your temporary situation, unless you are pulling a permit and getting inspected, extension of the existing system would seem reasonable.
You should replace it with a more modern grounded wiring method as soon as is practical though.
Happy New Year!