For this guide i will use the Hannes Convertor 2.0, available for download from this site, by going to the downloads section or clicking HERE!!
All you need to do, is download that pack and open it up. Once open you need to click the button on the top left (it looks a bit like a plug). This is where you will select your database, that you wish to edit.
1. You will need to open up the table DYN_cyclist.
2. Once you have opened the table, search for the rider(s) you wish to edit, and locate the "value_i_num_day_races" column. It is near the end (far right), so i suggest you start searching from the end.
3. Enter in your desired amount of race days.
4. Save using the button at the bottom of the screen, then the button at the top (looks like a floppy disc), select which savegame to overwrite then when the window appears showing the tables you opened, make sure you click on the ones you have edited before click OK, otherwise no effects will be noticed.