Changes a balance group's metadata, access, manager, closing date and how it renews.
It is the only way to change ends_on, recurrence_unit, recurrence_every and
base_amount_cents after creation. A funded budget's balance moves only through
POST /v1/budgets/{id}/top_up and POST /v1/budgets/{id}/withdraw; a tracking
budget's planned amount changes through PATCH /v1/budgets/{id}/amount, which moves
no balance. currency and mode never change. Only the fields sent are touched.

Access

• name, description, access and ends_on: admin / budgets_manage users, or
  the group's manager ("Encargado") or co-manager. Anyone else gets 401.
• manager_id: only admin / budgets_manage; otherwise 403
budgets/cannot_change_manager.
• recurrence_unit, recurrence_every and base_amount_cents: only admin /
  budgets_manage, since they commit the company's balance every period; otherwise
  403 budgets/cannot_change_recurrence.

Sending the value a field already holds (e.g. resubmitting the whole form) isn't
changing it, so it needs no extra permission.

Periods

A change to the periodicity or the base amount applies from the next period: the
period in progress keeps its period_ends_on and what it has. Turning recurrence on
for a budget that didn't renew counts its periods from its creation date; sending
recurrence_unit: null stops the renewals and the period in progress goes on with
what it has. A new ends_on (or null) reopens a budget whose closing date came but
was still closing.