If there are an even number of lamps, and you want them to be a lot dimmer, you could divide them into two groups, with the lamps in each group wired in parallel, but the two groups in series with each other. Note that if any lamp fails that would cause all the other lamps in its group to become brighter and those in the other group to become dimmer. If the lights were near rated voltage after having been wired in series, having the lights that were in the same group as the failed one get brighter could cause a cascading failure, but if each bulb is rated for the full circuit voltage that shouldn't be a problem.
Note that the transformer and all equipment should be perfectly happy with this approach, but that it will probably cut brightness by 75% or so [it will probably cut power consumption by somewhat less than 75%]. Whether that is acceptable would depend upon your desired look.
This particular site doesn't support a schematic-drawing tool, but it would be possible to wire a double-pole double-throw switch to select between normal and greatly-reduced brightness. Such a design would not be appropriate with 120VAC, but shouldn't be a problem with low-voltage wiring.