insert digits between 2 wordlists

[Snoopy]

Yep, had the same issue. Problem is that you cannot pipe the results in a combinator attack. You can only pipe them into a single brute force attack. See my post and answer here:
https://hashcat.net/forum/thread-10680.html

One solution I can think of, would be to first run a combinator attack, with a left rule that you prepend some special character, then pipe that result (word1^word2) into a brute force attack with a rule file that tries to replace this special anchor character "^" with 00,01, etc.
The below is one way to go about it, it works.

Step 1), run a combinator attack, with a rule that works on the left side to append character "^"

Run .hashcat.exe -a1 --stdout wordslist1.txt wordslist2.txt -j $^

Step 2), pipe the output into a brute force attack (attack mode 0), with a special rule to replace all occurrences of "^"with two digits. If you have this character in your word lists, make sure to replace  "^" with another character in the rule file.

Example of such a rule replace_anchor_with_dd.rule
s^01
s^$02
s^$03
... (continue this password up to 100), I added it to this post

In general, I think it would be great if there would be support for piping into a combinator attack. It should not be hard to implement this at all. just like you know have -j and -k to indicate on which side a rule should be implemented, maybe we could use -l -m to indicate which side piped input needs to be places.
Just mo 2 cents.

feel free to open a github issue for this idea (new feature)