Can op codes be used instead of signatures? Are there any op codes or combination of opcodes that can be used instead of a digital signature when creating a transaction?
Existing signature schemes in Bitcoin are already implemented as opcodes (OP_CHECKSIG and OP_CHECKMULTISIG in particular), so this question's formulation seems a bit off.

If you don't mind a transaction whose outputs can be taken by anyone, this is trivial - you can just create an output with a script that does not use any signature checking opcodes.

Perhaps what you want to ask is Is there a way to create secure transactions without using any of the explicit digital signature opcodes?.

The answer to that is almost certainly no. You would effectively need to implement a digital signature scheme by hand, rather than relying on the provided ones. Digital signature schemes are remarkably complicated, and likely far beyond what is possible inside Bitcoin's current scripting language.