A cable that was bought too long or later hangs too low can be shortened at the ceiling rose without rewiring the whole light. The effort is manageable as long as nothing needs changing at the lower end (lamp holder) – shortening is done only at the top, at the ceiling.
Power off and check the starting point
Switch off the circuit breaker for the circuit concerned at the fuse box, and confirm with a two-pole voltage tester at the opened ceiling rose that there's no voltage left. Then carefully lower or support the light and slide the ceiling rose cover down so the terminal and strain relief are visible. Before disconnecting, note which core (L, N, PE) was in which terminal position – with three identical cores, that's no longer obvious at a glance once they're released.
Shortening the cable
Release the cores from the terminal, open the strain relief, pull the cable up out of the ceiling rose by the desired length and cut off the excess straight with cable cutters. Rule of thumb: better to leave 2 to 3 cm extra than to calculate it exactly, because you lose a bit more when stripping. How much cable you need in total can be double-checked beforehand with Calculating cable length.
Strip again
At the new cable end, remove about 8 cm of the outer sheath and strip each of the three (or two) cores individually by 8 mm (10 to 11 mm for push-in terminals – it's stated on the terminal itself). With fine-stranded wire, as fabric cables usually have, ferrules are worth it: they stop individual strands from sticking out of the side of the terminal and causing a loose contact later. Described in detail in Stripping fabric cable.
Reconnect the terminals and fit the strain relief
Put the wires back into the terminal in their original order (L-L, N-N, PE-PE) and screw them tight, then tug gently on each wire to check it's firmly seated. Next, position the strain relief so it grips the cable just below the end of the sheath – it has to carry the full weight of the light, not the terminal. Tighten it firmly and give the finished cable another good pull: if the cable moves in the strain relief, it isn't tight enough. More on how terminal and strain relief work together in Fitting a ceiling rose.
When a new cable makes more sense
Shortening is worthwhile if you want to lose between 10 cm and about 1 m. For bigger differences – say, if 3 m of cable is to become 1 m – a new cable cut to size is often the cleaner solution: the leftover piece of cable sold by the metre can be used elsewhere (e.g. for a plug-in light), and you don't also have to re-do the wiring at the lamp holder end if it would need shortening there too. If the fabric sheath is visibly aged or discoloured, a new cable also makes more sense than shortening the old one. Choose cable sold by the metre by colour and cross-section under Fabric cable.
Safety note
The shortening itself (cutting the cable to length, stripping it, re-wiring it in the light's ceiling rose) you can do yourself if the light is connected by a plug or terminal block and you disconnect the power first. The actual connection to the fixed ceiling wiring – for example if the flush box is also opened – remains a job for a qualified electrician. If you'd rather do without a ceiling connection altogether, Plug-in light without a ceiling connection shows the simpler route.
Tools needed
To shorten it you'll need: a two-pole voltage tester, cable cutters or a sharp electrician's knife, wire strippers (combination pliers will do; an automatic one set for 0.75 mm² is more comfortable), a small screwdriver to fit the terminal and, optionally, a ferrule crimper for 15 to 20 euros. The whole job takes 15 to 20 minutes on a familiar, easily accessible light; the first time you take apart an unfamiliar ceiling rose, allow more like 30 minutes, because you first have to work out the design and terminal type.
If you end up needing a new piece of cable in the right colour and length, you can order it by the metre directly in the configurator.