Is it appropriate to wear an honor stole/cord to my doctoral hooding and convocation?
Formal regalia for convocations are highly stylised - even the side to which a tassel falls can have meaning. It would not normally be appropriate to wear representations of achievement that are unrelated to the degree you are about to receive.

If the honor stole/cord has particular significance to you, you can write to your university to explain your situation and to ask for permission to wear it at your convocation. You should then abide by their reply.