Is it possible to force the tokens to be only in lower-case letters and numbers? In other words no capital letters?

Might not be exactly what you are looking for, but you can always upload a csv file into the token table with tokens that you chose.

I was kind of hoping that I did not have to generate 30,000 unique tokens by myself. But of course I can generate them in an older version of limesurvey and then import the csv fil.

allan031 wrote: But of course I can generate them in an older version of limesurvey and then import the csv fil.

When did Limesurvey changed the behavior of generating tokens?

Perhaps a feature request to add settings via GUI or configfile for valid pattern with tokengeneration.
That's common when finetuning password generation.
keepass.info/help/base/pwgenerator.html#pattern