Doubt from coordination compounds

In my notes it is said that Co3+(cobalt (3+)) can even make weak field ligand to strong field ligand .
Ex : In [Co(ox)3]3- Co 3+ converts oxalate into strong field ligand .
Does Co3+ always converts weak ligands to strong ones..If not pls say the exceptions.
Is there any other metal ions which does like Co3+....pls do list them ?

Co3+ will make oxy compounds as strong ligand but for halo it is still weak.

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Co^+3 form low spin complex except SCN^-1, S^-2 and N_{3}^{-1} i.e. azide

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