Section 26A. The assessors, or selectmen acting as assessors, may employ counsel at the expense of the city or town in all proceedings under chapter fifty-eight A; provided, that if such city or town maintains a city solicitor or town counsel the assessors, or selectmen acting as assessors, shall not employ other counsel but shall use such solicitor or counsel therefor, whose expenses incurred shall be paid from his general appropriation. The foregoing restriction on the right of the assessors to employ counsel for such purpose shall not apply in case the town has made an appropriation covering the employment of counsel therefor.