# [Red], 80 bytes

 func[s][repeat n length? s[if parse/case s[any[copy t skip n t]][return on]]off]

[Try it online!][TIO-jz8bthxa]

[Red]: http://www.red-lang.org
[TIO-jz8bthxa]: https://tio.run/##hZIxb4QwDIX3@xU@pqtE1bFqly4dbm3FhjIkxNwhuDhKghC/ntqNiqJT1X4Ttt97JIaAdvtE26pD/wpbP7uujaoN6FEncDChu6TrG8R26MHrEPGp0xG51m5tO/IrJIjj4FmblBjTHByQU4r6Xm0@DC5BD9X5jDgxRHUNsCxEIUyTtcdjddhFTdOEEIZh8N6zFhEBIMbIJT9rrcdxLOQfzMzwQFuGvUFqn@3ilwBJkAjJkBBJKWOeM4@ZmPEZzOjMmCm8Lz8UPVEac9fITWO67n4g3V1dfZ@hkJx5a1TDQmGy/6@Kv9r4y4v3AxSzd0s0z8aIV1Ykd5UblnY4WcIIjvhXQLSQCAzCVTs7oX0olCe8@bRCTNy41PCna/sC "Red – Try It Online"