To change start max HP, find this line in 'parameters.fos' and change the value. (For example change 15 to 115 to add 100 extra starting HP)
_param_[ST_MAX_LIFE] += 15;
To change XP per level mess around with the following function, for example change 1000 to 10. (I did not test this answer, so if not correct, look for something similar in code.)
int NextLevelNeedExp(Critter& cr) // Export
int level = cr.Stat[ST_LEVEL];
return NUMERICAL_NUMBER(level) * 1000;
You can also ask questions on discord #modding text channel, I don't always check forums.