I am not sure if it was intentional, but custom characters cannot be created with Excellent stats.   In the "src/variables.gd", the maximum is 6.

var maximum_factor_value = 6

However, the "CharacterCreationMainModule.gd", two lines have 5 as their setting.  Basically, the interface panel won't permit an increase.

func RebuildStatsContainer():

................................

            if i.code in ['growth_factor','timid_factor','tame_factor'] && mode == 'master':

                preservedsettings[i.code] = 5

func stat_up(stat):

    if preservedsettings[stat.code] >= 5 || unassigned_points == 0:

Starting with e.g. Physics 6 would not only take a bonus from a few classes but also it wouldn’t make sense when a person that barely know how to hold a sword  (no weapon based class like fighter or archer) had a body refined as a highly skilled swordsman.

That is at least my opinion in this.

This is intended.

you can upgrade the characters at the slave shop to exellent, but from 5 to 6 it is in the beginning expensive