I'll give a quick explanation, let me know if you need more detail.
1) Extract the race.m2
2) Load the .m2 with the model resizer tool in Glitchy's MES
3) Enter the multiplyer (I used 1.35) and click shrink model
4) Load the .m2 with Glitchy's Animation Editor
5) Go to the run animation and lower the speed (I changed it to like 5.2 or something)
6) Delete the old .m2 from your custom patch
7) Import the new .m2 with the same treepath as the old one