Thanks alsetalokin4017 for your explanations!
Could you say a bit more to 4.? How can I measure the bw that way?
There is more information on measuring bandwidth in the original, very long, DS1054Z thread and probably in other threads on the forum too.
"Quick and Dirty" you will be looking for a 3dB reduction in the amplitude of a sine wave signal applied to the scope, as this is one definition of scope bandwidth. So you need a signal source that can actually put out a constant amplitude sine wave in the range of 50-150 MHz, connect it via proper cabling and terminations to the channel, and carefully monitor the amplitude displayed as you sweep the frequency of the generator. When the displayed amplitude has dropped 3dB from the known input value, you've found the 3dB rolloff frequency and then that is your "bandwidth" according to that definition.
For a rough comparison you could supply a 100MHz signal to the scope, then use the SCPI commands to "uninstall" the unlock key, reboot, "install" the key, reboot and see if your displayed amplitude of the signal changes much.
I have connected the trigger out to channel 2 while on ch 1 was a signal. I got a rise time of 2.6ns... does that help in any way?
Probably not because you don't know whether the risetime and other waveform features are a result of the process generating the signal or the scope's response to it.
Still, you could perform the comparison by uninstalling and reinstalling the unlock key and looking at the displayed signal for changes, as I noted above. You can store the waveform as a reference waveform and compare the waveforms before and after unlocking that way.
I have not performed such comparisons myself -- yet. I've just been taking the word of those with better signal generators than I've got, who have reported the increased bandwidth after unlocking.
(I do have an HP 8640B over in the corner buried under some other stuff; I suppose I should dig it out and fire it up to do some testing of my own, but the thing is huge and heavy, and it would mean cleaning up and rearranging my whole lab to be able to use it ...)
