criminal case investigation officer change

rarely session judge will not say for changing of investigation officer (except in exceptional cases)
first accused can be involved again in investigation through services of notices under 91crpc by investigating officer. even if accused has not joined the investigation after serving notices under 91crpc than investigating officer can serve notice under 41A which compel any person to join the investigation.
secondly- any investigating officer is changed only by higher administrative authority. executory body involved on changing of IO. any aggrieved party can move letter to commissioner/SSP/SP for changing investigating offices by describing reason for change.

With all due respect to your response, Firstly notice under Section 91 CrPC cannot be issued to an accused person, if it has been issued then one needs to challenge the same.

Secondly if complainant has some material that IO is not investigating in a fair manner then apart from writing to higher officials of police department one can also approach the concerned magistrate by filing an application.

Regards