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I took the levers off and replaced them with a set of Shimano levers yes. It works well enough for my commuter. My main issue was play in the indexed sunrace lever, which meant you had to move the lever after it had clicked in order to get the chain to run smoothly.
It might have been an issue with improper cable tension, now that I think about it, but I much prefer the friction setup.
Are you saying you can modify the sunrace levers?