if you know an engineer personally, they can just use their laptop or an app on their iPhone/iPad or whatever to do the DLM reset. Tough luck for anyone else who doesn't know an engineer personally. I'm not sure the engineer would be strictly supposed to do that if they weren't visiting in an official capacity organised by your ISP, and of course, if it were an official visit organised by your ISP, you couldn't guarantee which engineer you'd get.
ejs is correct.
1) There isn't any way of allocating or requesting a particular engineer to a job. If a new fault is reported then it just goes into a pool that automatically allocates. On required visits for same fault you are most likely to be allocated a different engineer. However I think there is something in place that an engineer who has previously visited for same fault can pick up again if they want. I know with my HR fault, I had about half a dozen different engineers, but the one who finally fixed it gave me a number to ring if there was any more problems over the next few days so he could pick up any requested revisit.
2) A reset can only be performed by a visiting engineer if he has found and corrected the fault. Openreach has a very strict stance on the reset procedure - all DLM resets are logged against the engineer who performed it and routinely checked for abuse. I'm sure that last year BS said last year or so that a new procedure had been put in place which specifically checked for abuse of DLM resets and that any found could result in disciplinary action for the OR engineer. 
3) ejs was actually trying to help when he made the 80/20 suggestion - because that is the only way that we know of whereby a DLM reset could automatically be re-triggered.
A change of product ie 40/10 to 80/20 will cause a reset. Change of ISP doesn't.
There is actually a process called 'Named engineer' in place whereby the EU can pay more (I think it's £50) to get a particular engineer out.
Regarding DLM resets. Kitz is bob-on (along with other members inputs) in that we are strictly told not to perform a reset unless a fault is found and rectified. Now this is a grey area for me, as I only yesterday picked up a fault that had seen the EU go from a constant 40Meg down to 1.8Meg. It happened on just one day. After quizzing the EU, he mentioned that the very same day the electric board had been changing out a sub-station opposite his house.
Now all the expected tests passed, the installation was up to par ...... there was nothing to fault if you will. But experience obviously tells you that this was a one-off event and as such I did do a reset and he was back at 40Meg and completely CRC/FEC free on a 15min test.
Point I'm trying to make is we can do a reset whenever we choose, but to just do so nilly-willy may attract the attention of 'Them above'. Quite how well the reset system is monitored, I wouldn't know but in today's BT, there
will be somebody sat there collating stats !!!!
