Yes, possible.
@error_messages = {
:password=>["can't be blank", "Password is required."],
:"addresses.firstname"=>["can't be blank","Firstname is required."],
:"addresses.city"=>["can't be blank", "city is required."]
}
@error_messages.each do |_,v|
v.delete( "can't be blank" )
end
@error_messages
# => {:password=>["Password is required."],
# :"addresses.firstname"=>["Firstname is required."],
# :"addresses.city"=>["city is required."]}