3rd Counselor access on lds.org

Recently a 3rd counselor has been called in both our primary and relief society presidencies in our ward. Both presidencies have asked that the 3rd counselor be given the same access rights as the other counselors in the presidency on lds.org. Although the 3rd counselor shows up as part of the presidency on lds.org, it is a custom calling and therefore does not carry the default access rights assigned to the standard counselor callings in the presidency. I couldn't find a way to alter the access rights of the 3rd counselor the same way I would be able to in MLS. Is there a way to do this?

Giving online access to a third counselor is not possible. However, a workaround for the Relief Society would be to add the extra counselor as a Relief Society assistant secretary, which is a standard calling and has access (though assistant secretary isn't a standard calling for Primary).

If you have a large number of sisters in your Relief Society, perhaps a better and more Handbook-aligned approach would be to split your Relief Society into two separate Relief Societies (Handbook 2, 9.9.1). This is commonly done in young single adult wards because of the number of adult sisters, and everything works smoothly in Leader and Clerk Resources.

I've heard of wards dividing the Primary as well, but I can't find reference to that anywhere in the Handbook.

No. 3rd councilors are going beyond the Handbook and are not supported. This is not an area where local leaders have flexibility.