I don’t know anything about changing the sensitivity, so I waited to see if others would reply. Since nobody did, let me add some related stuff, even if not a direct answer,
I found since my OP that @krlaframboise’s Simple Event Logger shows you actual accelerometer data, the only app I personally know that will do that. Here is actual data for yesterday and today:
> **Put item in mailbox 3/14**
> 03/14/2017 10:58:46 init acceleration active
> 03/14/2017 10:58:46 0 threeAxis -821,60,273
> 03/14/2017 10:58:47 1 threeAxis -671,-1121,238
> 03/14/2017 10:58:48 2 threeAxis -1017,46,-35
> 03/14/2017 10:58:49 3 threeAxis -1020,34,-34
> 03/14/2017 10:58:50 end acceleration inactive
> 03/14/2017 10:58:50 0 threeAxis -1010,37,-36
> **Mailman comes 3/14**
> 03/14/2017 12:12:07 init acceleration active
> 03/14/2017 12:12:07 0 threeAxis -1243,-101,-71
> 03/14/2017 12:12:08 1 threeAxis -1019,29,-84
> 03/14/2017 12:12:09 2 threeAxis -1018,32,-37
> 03/14/2017 12:12:10 3 threeAxis -1013,39,-32
> 03/14/2017 12:12:11 end acceleration inactive
> 03/14/2017 12:12:11 0 threeAxis -1016,37,-31
> **Mailman comes 3/15**
> 03/15/2017 11:25:57 init acceleration active
> 03/15/2017 11:25:57 0 threeAxis -1153,99,-111
> 03/15/2017 11:25:58 1 threeAxis -1012,35,-15
> 03/15/2017 11:25:59 2 threeAxis -1016,28,-35
> 03/15/2017 11:26:00 end acceleration inactive
> 03/15/2017 11:26:00 0 threeAxis -1020,32,-36
> 03/15/2017 11:26:02 init acceleration active
> 03/15/2017 11:26:02 0 threeAxis -1046,79,-172
> 03/15/2017 11:26:02 1 threeAxis -1285,70,-408
> 03/15/2017 11:26:03 2 threeAxis -1021,28,-41
> 03/15/2017 11:26:05 end acceleration inactive
> 03/15/2017 11:26:05 0 threeAxis -1016,34,-41
> 03/15/2017 11:26:06 1 threeAxis -1017,33,-29
It’s all straight from Simple Event Logger except I made the column with Init / End / elapsed seconds, as an attempt to explain what’s happening.
This is the first time I’ve looked at it much and it’s kind of interesting. Looks like you’re getting one reading a second for four seconds (including initial state reading) every time there is an Event. It appears to return to the same approximate location for the end of event; not sure why there were two Inactive rows at the very last. Might be interesting to plot… is the excursion from centerpoint tamping down over the three seconds, to zero?
Maybe I am indirectly helping you by showing that there are values that can be intercepted, and you might be able to do further action based on the size of the excursion from accelerometer resting position. (The one perhaps shown by Inactive coords.)
Of course, this is if you are able to and care to do all the heavy lifting. I think you said you’re not, eh? 
But maybe others can profit from this.
The data above is only what I just grabbed. Maybe Activity can last for an hour if somebody kept shaking it, etc. I have no idea. I have about 500 threeAxis records from the past two months, if anyone wants to see more data, or what someone else’s looks like.
I am paging @joshua_lyon of SharpTools because that is one nifty app for working with ST. Maybe he can comment on whether the accelerometer can be worked with, with SharpTools or otherwise.
I also just made a very long post about using acclerometers for sensing mailbox mail delivery here, if anyone is interested.
Hope this helps!