Other major chess database programs allow this, but I am curious if SCID has this "print as repertoire" function. Opening report in SCID creates an ECO table from multiple games, but I'd like to instead use a single game with sub-variations as input.
With pgn-extract, you could "Output each variation as a separate game (--splitvariants)"
The --splitvariants flag will output each variation of a game as a separate game. The headers of the containing game are reproduced for each variation, except for the Result tag, which is replaced with "*" to indicate that it is not necessarily a complete game.
The flag takes an optional positive integer to limit the depth of variants output as separate games. For instance: --splitvariants 1 will only output separate variant games for top-level variants. Others are suppressed from the output. A value of 0 is used to output all variants and may be omitted.
Create an small database with your games with variations of interest. Export to pgn and process with pgn-extract. Import again those games to SCID and use Opening Report with this temporal database.
First of all, I do not know if trying the feature Opening Report on a single game (or a database composed of a single game) would show the variations in the ECO tree. If you have not tried it, this would be my first step.
I also don't know if the ECO table can be directly printed as on ChessBase (it certainly is a great feature), but what you can do, albeit being a bit more of work, is to make a SCID database rewriting all the variations as whole (unfinished) games, and then use Opening Report to get the desired ECO tables.
What I mean by this is that if I have a game that goes:
1. e4 e5 2. Bc4 (2. Nf3 Nc6 3. Bc4) Nc6 3. Qh5 Nf6 4. Qxf7#
Then the variation shall be included in the database and this game would be split into two, the main line and the variation, when being rewritten. When using Opening Report on this variation filled database, you will certainly obtain the ECO tables (and more).
This should not be extremely difficult and hopefully not long. I suggest you take a look at this video, as here the theme of easily including and saving variations in a game is a bit discussed (although the main purpose of the video is to use SCID to develop an opening repertoire).