Actually for the Sweboz reforms all you need to do is edit the EDU (export_descr_units.txt).
Find the various entries for reform units and replace the "siege" tag in the weapon line with "simple".

Code:
;496
type             germanic cavalry marhathegnoz
dictionary       germanic_cavalry_marhathegnoz      ; Marhathegnoz
category         cavalry
class            heavy
voice_type       General_1
soldier          celtic_cavalry_brihentin_remimairepos_lavotuxri_marhathegnoz, 25, 0, 1
mount            medium horse
mount_effect     elephant -4, chariot +2
attributes       sea_faring, hide_forest, hardy
formation        1.5, 4, 3, 6, 4, square
stat_health      1, 1
stat_pri         6, 30, no, 0, 0, melee, siege, piercing, spear, 160 ,0.33
stat_pri_attr    ap
stat_sec         12, 15, no, 0, 0, melee, blade, slashing, sword, 0 ,0.225
stat_sec_attr    no
stat_pri_armour  11, 11, 2, metal
stat_sec_armour  0, 0, flesh
stat_heat        4
stat_ground      0, 0, -2, 0
stat_mental      16, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay  0
stat_food        60, 300
stat_cost        1, 4034, 1009, 95, 444, 4034
ownership        germans
This also works with the carthage, seleucid and saka reforms as well.