No one else seems to want to answer so:
No. You are wrong.
FCL.910.FI FI — Restricted privileges
(a) An FI shall have his/her privileges limited to conducting flight instruction under the supervision of an FI for the same category of aircraft nominated by the ATO for this purpose, in the following cases:
(1) for the issue of the PPL, SPL, BPL and LAPL;
(2) in all integrated courses at PPL level, in case of aeroplanes and helicopters;
(3) for class and type ratings for single-pilot, single-engine aircraft, class and group extensions in the case of balloons and class extensions in the case of sailplanes;
(4) for the night, towing or aerobatic ratings.
An FI with Restricted privileges may only teach for the above (provided they are appropriately qualified) at an ATO and under the supervision of a nominated FI.
No mention of teaching for an IR, therefore an FI(R) cannot; and, therefore, I very much doubt that any ATO would accept an FI(R) on to a course to gain a "privilege that may become valid later" after their restriction is lifted.
NB: I know that some people have suggested that an FI(R) may teach for anything (provided they are appropriately qualified) with the above only being a list of the types of "Instruction that must be supervised"
Good Luck if you rely on that interpretation !