Of course you'll get the prussian national ideas, which are by far the beast in the game, when you form Prussia but do you get back your good but not as good as prussian ideas if you form Commonwealth?
Actually no, you cannot form the Commowealth as Prussia, the decision is reserved to either Poland or Lithuania:
country_decisions = {
pol_commonwealth = {
major = yes
potential = {
NOT = { exists = PLC }
NOT = { tag = HLR }
[B]tag = POL[/B]
LIT = {
exists = yes
ai = yes
}
}
allow = {
adm_tech = 10
is_subject = no
stability = 1
is_at_war = no
owns = 262 # Krakow
owns = 257 # Warszawa
owns = 43 # Danzig
owns = 1841 # Marienburg
is_core = 262 # Krakow
is_core = 257 # Warszawa
is_core = 43 # Danzig
is_core = 1841 # Marienburg
senior_union_with = LIT
NOT = { num_of_unions = 2 }
MAZ = { exists = no }
}
effect = {
change_tag = PLC
inherit = LIT
if = {
limit = {
wielkopolska = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
wielkopolska = {
add_claim = PLC
}
}
if = {
limit = {
malopolska = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
malopolska = {
add_claim = PLC
}
}
if = {
limit = {
belarus = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
belarus = {
add_claim = PLC
}
}
random_owned_province = {
limit = { culture = polish }
add_base_tax = 1
}
add_prestige = 25
}
ai_will_do = {
factor = 1
}
ai_importance = 400
}
lit_commonwealth = {
major = yes
potential = {
NOT = { exists = PLC }
NOT = { tag = HLR }
[B]tag = LIT[/B]
POL = {
exists = yes
ai = yes
}
}
allow = {
adm_tech = 10
is_subject = no
stability = 3
is_at_war = no
owns = 272 # Vilna
owns = 276 # Minsk
owns = 280 # Kiev
owns = 1941 # Turov
is_core = 272 # Vilna
is_core = 276 # Minsk
is_core = 280 # Kiev
is_core = 1941 # Turov
senior_union_with = POL
NOT = { num_of_unions = 2 }
MAZ = { exists = no }
}
effect = {
change_tag = PLC
inherit = POL
if = {
limit = {
wielkopolska = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
wielkopolska = {
add_claim = PLC
}
}
if = {
limit = {
malopolska = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
malopolska = {
add_claim = PLC
}
}
if = {
limit = {
belarus = {
NOT = { owned_by = POL }
NOT = { owned_by = LIT }
}
}
belarus = {
add_claim = PLC
}
}
random_owned_province = {
limit = { culture = lithuanian }
add_base_tax = 1
}
add_prestige = 25
}
ai_will_do = {
factor = 1
}
ai_importance = 200
}
}