OK, I see. Thanks for that diagram.
Yes, your modified schematic is what I was suggesting, to convert a normally open circuit to normally closed.
Using an optocoupler driving a transistor is not a perfect solution. As Harald just pointed out, you will have some voltage dropped across the transistor. If you connect several "contacts" in series, these voltage drops will add together, and there may not be enough voltage remaining to activate your final relay coil reliably.
With my suggested normally closed circuit, yes, you will also get some leakage current when the transistor is OFF. Whether this is a problem or not depends on the relay coil that the contacts are driving. A small amount of leakage current won't cause enough voltage across the final relay coil for it to pull in, but it will waste power.
Can you modify the part of the circuit that has the relays connected in series driving another relay? If so, you can replace those relays with optocouplers, connect the optocoupler transistors in series, and use them to switch a transistor that's powered from the 48V supply, which can drive the relay coil. That would be a simpler solution if it's possible to modify the circuit in that way.
If you need a completely self-contained circuit that will plug into any of those positions and replace an old relay, another option might be to use a standard electromechanical relay specified for a lower voltage, and add a resistor in series with the coil so that it will operate from 60V. You should be able to find 48V relays with sensitive coils that could completely replace the original relays. You could get relays with changeover contacts, so you could use the normally open contact or the normally closed contact. This would be your simplest option.