The level 2 wording is deliberately expository.
The intention is that you can play any response to 1NT with or without intervention
You can play all the standard responses, but (apart from negative responses to a Strong 1 !c opening, or a catch-all 1NT response) you cannot play artificial weak bids in response to a one level suit opening.
Firstly, yes, Lebensohl is permitted at level two: 2NT in that situation is a relay to 3C with additional information likely to follow.
At level 2 there are restrictions on overcalls of 1NT which don't exist at level 4. For example, where a bid suggesting a suit contract is made, it is required that there is at least one known suit, which makes a Mutli-Landy 2D overcall, showing either major suit, illegal. A 2NT overcall showing both minors is legal but a 2NT overcall showing either both minors or a strong two-seater in any suits is illegal. These are all fine at level 4 where any agreed method over 1NT is legal.
Comments
The level 2 wording is deliberately expository.
The intention is that you can play any response to 1NT with or without intervention
Firstly, yes, Lebensohl is permitted at level two: 2NT in that situation is a relay to 3C with additional information likely to follow.
At level 2 there are restrictions on overcalls of 1NT which don't exist at level 4. For example, where a bid suggesting a suit contract is made, it is required that there is at least one known suit, which makes a Mutli-Landy 2D overcall, showing either major suit, illegal. A 2NT overcall showing both minors is legal but a 2NT overcall showing either both minors or a strong two-seater in any suits is illegal. These are all fine at level 4 where any agreed method over 1NT is legal.