I'm actually talking about a CVT transmission here. I understand that CVTs don't actually have gears, so what I mean by "first gear" in this case is switching to manual mode and accelerating the car to 60-70 KPH without shifting up.
Can this damage the transmission in any way?
As long as you don't exceed the maximum speed (revs) of the engine you should be ok. If you do, then forces acting in the transmission can exceed design limits maybe causing damage.
Modern engines have a way to reduce fuel injection when the engine is at danger of over-revving. So, with modern computer-controlled engines, there is no way to accelerate past the redline. What you described will absolutely not damage the engine or the transmission, but probably isn't recommended to be done on a cold engine too often.
The most typical way to over-rev an engine on a manual transmission car happens when downshifting an engine to a gear that causes the RPMs to go past the redline. You don't have a real manual transmission but rather a computer-controlled CVT, so I suspect if you first accelerate to 100 km/h and then try to downshift to first virtual 'gear', it will not do the downshift.
So, abusing your engine and/or transmission is indeed very hard with your setup.
