Get a bit of chunky aluminium strip (or stainless steel, but aluminium will be much easier to work with|) to bridge the gap between the original fixings and the lowered shower rail.
Conduit box at existing location, drop down in 25mm conduit, conduit box with dome lid and horizontal rail into 25mm dome lid. If you can't get chrome conduit stuff build it and take it to a chromium-plater.
Depends on how "handy" you are. Personally, I would bite the bullet and redrill and fill. But you could make a pair of fishplates, bits of sheet material at least 10 mm thick, same width as the existing fitting, and about 140 mm long. Round the ends to make it look neat. At the top, drill three holes to take the existing screws. At the bottom, drill a single hole to take the curtain rod. You would probably want to bed it on a bit of silicone or similar to prevent it moving away from the tiles.
Materials: timber or plywood is most readily available and easy to work, but you would need to varnish or paint it effectively. If you happen to have any offcuts of Mermaid board or similar, that would be ideal. Or you could buy sheet Polythene, PVC, Nylon, etc from a specialist plastics supplier. Or a piece of brass or even stainless steel if you have access to such things.
I cannot really work out how you have used that particular fitting on a tiled wall, to support a shower head rail. Surely the shower head rail needed to be vertical, and on a wall that fitting will provide an horizontal bar?
Use a piece of 3mm or 4mm sheet aluminium. Make it the width of the fittings and the necessary height to give the drop you require. The ends should be exactly the same profile as the footprint of the fittings, so use the fitting as a template for the rounded ends. Drill the holes at the top to take the screws that will go into the wall. Countersink the holes. To hold the fitting use self tappers with heads that fit the countersink in the fitting. Use over-long self tappers then grind off the excess length on the other side so it is flush with the aluminium. The holes should be positioned so that the rounded end of the sheet is exactly flush with the edge of the fitting. Sand the completed aluminium to provide a key. Spray with aluminium primer. Paint matt grey, at least six coats.
Leave the original rail up and string, rope or wire or gaffer tape another parallel rail below to hang the curtains on.
Inform management that the issue has been resolved with a workaround. Do not leave promises to make better, ye could say 'monitoring the situation' without much risk, and if the string/wire/tapes breaks just repeat the original fix.
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