Oxidation numbers and transition metals

Confused with this question:
Manganese forms a complex with carbon monoxide, with the formula Mn2(CO)10. What is the oxidation number of manganese in Mn2(CO)10?

The answer is zero.
The oxidation states of all uncombined elements is zero.
Carbon monoxide has no charge.
The total charge on a species is the sum of the oxidation states.
Total dcharge = zero
Charges of the ligands = zero
Hence, oxidation state of Mn = 0

Ligands always have a charge of 0?

Ligands always have a charge of 0?

The answer is zero.
The oxidation states of all uncombined elements is zero.
Carbon monoxide has no charge.
The total charge on a species is the sum of the oxidation states.
Total dcharge = zero
Charges of the ligands = zero
Hence, oxidation state of Mn = 0

Cl-, OH-, C2O42- et.al. happily are ligands (they all can form dative bonds to the central metal ion).

Would these ligands affect the charge of the central metal ion?

No, but when they combine to make a complex ion, you start talking about the charge on the complex ion, rather than the charge on the metal ion which you refer to as the oxidation number.