max Discharge current of li-ion battery (temporary)
Does cooling the cell (for example in a Tesla battery pack) increase the max current that the cell can provide without overheating

Yes. But it's a fallacy that you can do much with that: the energy used for cooling has to come from the battery. So, this only works as long as the cooling efficiency is higher than the heat losses.

I was wondering if 18650 Li-ion cells can be temporarily discharged at a higher discharge current than their max rated discharge current? (provided the battery is adequately cooled/temperature stays below 50 degrees celcius)

&quot;rated&quot; means &quot;rated&quot;. So, if you want to be safe: no.
Practically, operating a LiIon battery warm is desirable: while it increases ohmic losses, it greatly increases charge carrier mobility, which is where most of the internal resistance comes from. So, you need some temperature to even draw a high current. But. 50 °C might be totally sufficient for that. If you can keep it at that temperature internally without freezing the outer half of it, you might just be fine. Don't forget that &quot;can be operated heat-damage-free&quot; doesn't mean &quot;damage-free&quot;: you might still have electrode migration, gassing, … at high curents.
Also, nothing says the battery will let you draw any current higher than rated: There might simply be physical limits, and in a logically designed cell, these wouldn't be extremely far beyond thermal limits – no use to make a cell that is capable of more current than its thermal design allows for. Better use the space / weight / cost you saved for more capacity / lighter battery / cheaper battery.