This has to be a guess as there is no standard way to wire. But it would seem the switch back box is being used as a junction box so all blues should still go into a connector block.
Permanent line in Com and switched line there seems to be two will go into L1. If you use L2 it would still work but likely wrong way around i.e. up for on instead of down.
I have removed all my dimmer switches because. 1) Should not be used with tungsten quartz as the shorten bulb life the temperature of envelope is critical they should not be run cold. 2) Using any switch mode power supply the dimmer needs to 'talk' to the unit often meaning has to be either leading or lagging to match each other. 3) Because bulbs are coiled coils they have some induction if not matched the bulb can start pulsing. 4) Means you have to use very expensive CFL or LED and often the colour does not change so you no longer get the ambience given with the lower colour temperature. 5) Often when bulbs blow you get ionisation the flash when bulbs blow which in turn often blows the dimmer. 6) There is often both a max and min for bulb sizes with dimmers which it is so easy to forget about when replacing bulbs.
And the biggest one was after the first 6 months novality wore off I never dimmed the lights.
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