There is nothing in the Convention that says or implies, in any way shape or form, that access and return are mutually exclusive.
You can absolutely request both under the letter and spirit of the law and, indeed, the standard form used by OCI to file a petition under the Convention allowed for just such a request to be made.
That said, as a practical matter, the court may be more leery about giving you interim access while you are still requesting a return as it implies a desire to remove the child from the country, but there is no sound legal basis for this bias (unlike the explicit pro-mother bias that exists in every one of Mexico's 30 some states and it's federal district.)
In practice though access rights under the Convention tend to be a nullity. My son's mother skipped somewhere around a hundred court ordered visits and only had to pay a $100 or so fine one time after months and months of her flagrantly defying court orders.
One things for certain...
If you switch your case to a purely access case, OCI will mark the abduction (ie "return") case as resolved and your son will no longer appear in the non-compliance reports (which are all but worthless themselves.) Which, of course, is the reason they like to push this "option" to LBP's... particularly those with long running unresolved cases.
