This file assigns the text descriptions for the defined reputation values from 0 to 20.
In IWD TotL we have:

2DA V1.0
-1
           VALUE
0          10366
1          10366
2          10366
3          10366
4          10366
5          18708
6          18708
7          18708
8          18708
9          10368
10         10368
11         10368
12         10368
13         10370
14         10370
15         10370
16         10370
17         10387
18         10387
19         10387
20         10387

where first column is reputation value and the second one is the string reference in the Dialog.tlk file.
I have not tried to make more or less reputation levels, however I suppose it is totally possible to make as many of them as needed.