Liverpool will probably play better then in the 1st leg because Real Madrid will start a weaker 1st team to try and prevent injuries to their most important players but Liverpool are not in good form and are in crisis so I do not expect them to win if Real Madrid put out a weaker team. 3 goal cushion away from home is too much to expect from this Liverpool team who struggle to keep clean sheets so I expect Real Madrid to get at least 1 goal in the 2nd leg.
Regardless of the great result and the big win in the first game, I really don't think that Real will send a weaker team in return and rest the main players.
Such a thing is done in the group stage of the competition when placement in the knockout stage is already assured, and not in the knockout stage of the competition.
Bigger surprises happened in the Champions League, do you remember Liverpool's 4-0 win against Barcelona after losing the first leg by 3 goals difference?
Chelsea almost kicked Real out of the Champions League last season after, like Liverpool, they lost the first home game by 3 goals.
Real will not rest any player and the best team will play against Liverpool, I have no doubts about that.
I expect a difficult and uncertain match, but Real is too experienced a team not to take advantage of such a good result from the first match.