Without a credible explanation of how you could have encountered every single ELV luminaire which has ever been on the market, and every single after-market GU10 lampholder, there's no way that your assertion that you know that the OP's would be safe if he changed the lampholder and ran them at 230V can be accepted.
Your advice has to be judged to be incorrect - there is no way that it can be assumed that you have encountered every one etc, so there is no way that it can be assumed that your advice must be correct, and not shamefully irresponsible.
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