And just to cover your back, Warn the customer that if for any reason it doesn't run properly after disturbing the injectors then its there problem, Not yours. Explain that the injectors are very sensitive and disturbing them can cause problems on the odd occasion.

I have never done the job myself but I have seen lots of garages do these and end up with lacking power, misfires etc. Most likely due to them cleaning the injector nozzles with a wire brush, but they never admit it.

Better safe than Sorry.