Yes....... But........ 750mAh and 800mAh are the capacity of the battery. More capacity means more power. The handset always assumes that the proper batteries are inserted. If it was designed for 800mAh then the handset puts a charge of 800 into the batteries. If a 750mAh is inserted instead, it will overcharge the batteries. Overcharging is not good for batteries. Each overcharge will lessen the life of the battery. The batteries may heat up too much which could be dangerous. In the vice versa case it might happen that the 800mAh batteries are always charged only upto 750mAh, giving you the same performance and not better. So it completely depends on the way the handsets are designed.
It is generally safe to use a higher capacity battery (1100mAh) with the same voltage (3.7V) in place of a lower capacity battery (1000mAh) in a device. However, always ensure the physical dimensions and connectors of the battery are compatible with your cell phone to avoid any damage. Use caution and if unsure, consult with a professional.
If, by 'larger battery' you mean one with the samevoltage but higher capacity - there's no reason why not. It will simply take a little longer to charge it. I swapped my 3.6v 600mAh battery for a 3.6v 1000mAh battery a long time ago - and the phone still works perfectly well.
Yes
no
Yes, you can use it if your device has a compartment big enough to hold it. The 2032 is twice as thick as the 2016.
As long as the batteries are putting out the exact same voltage, then yes you can use a battery with a higher ma rating.
The shaver will run a bit slower.
can use 1400mah battery to replace 760 mah
It is always best to replace batteries with identical batteries. However if the replacement battery has the same voltage and the same physical construction (so it will connect electrically) it can usually be used as a replacement. The mah rating (capacity) only says how long it takes to charge and how long it will run between needing a charge. However some charging circuits might experience problems if this rating is significantly different from the original.
Yes you can use C-cells ... they are the same voltage BUT, they will rattle around and loose contact. Your best bet is to get some more D-Cells.
Yes, that is acceptable.