A domestic mutual insurer, after being authorized to transact 1 kind of insurance, may be authorized to transact such additional kinds of insurance as are permitted under § 510 of this title, while otherwise in compliance with this title and while maintaining unimpaired surplus funds in an amount not less than the amount of paid-in capital stock required of a domestic stock insurer transacting like kinds of insurance, subject further, when first so authorized to transact an additional kind of insurance, in the case of insurers other than those to which § 511(a)(1) of this title is applicable, to the additional expendable surplus requirements of such § 511 applicable to such a stock insurer.