I'm going to take a punt and say you're after an automatic lookup, what you mean by "an additional row in my CSV file?" is a bit beyond us as you haven't mentioned an existing CSV file 😉
In this case I would put it into a lookup such as;
values.csv
Field, Value
A,2
B,1
C,2
I would then create an automatic lookup in my props.conf for that sourcetype;
[MYAMAZINGSOURCETYPE]
LOOKUP-values = valuescsv Field OUTPUT Value
In transforms.conf I would define the lookup...
[valuescsv]
filename = values.csv
Finally, you need to take into consideration how the Field value is extracted, presumably this is already handled in your instance but you need to make sure that is extracted BEFORE the automatic lookup.
Otherwise, you can now run a search on that sourcetype for a Value=2 to only see those values.
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