Well, the concept of virtus in itself is very complex and to offer a confirmed definition of the concept is incredibly difficult. When doing research on virtus during the period of Scipio Africanus/Cato you realise how not even the Romans had a complete definition for the term and it was more of a case certain acts being deemed to fall under the concept.

Virtus itself is thought to be associated with the Greek concept of aretê which is thought to have stood for excellence (simplified). Within early Greek works, such as Homer and Pindar, aretê is usually viewed as an aristocratic quality, dependent on birth and wealth and associated with military and political accomplishments. Plato and Aristotle both debated the concept within their works taking it away from the discussion of aristocracy, and it is Aristotles discussion in the Nicomachean Ethics (book 2) in which we would find a definition that is related to what we believe the Roman virtus stood for. For Aristotle (Nicomachean Ethics. 2.6):

Now virtue is concerned with passions and actions, in which excess is a form of failure, and so is defect, while the intermediate is praised and is a form of success; and being praised and being successful are both characteristics of virtue. Therefore virtue is a kind of mean, since, as we have seen, it aims at what is intermediate.

Aristotle therefore believed that virtue was found in the ability of a man to display the right characteristic at the right time. For example with fear, to feel it the correct amount was to be courageous. To feel fear too much was to be cowardly, and to feel it too little was to be rash. The ceoncept with this definition is something that can relate to what we know about the Roman concept of virtus - that being how one presented themselves.

 

To move on to trying to answer your question, the concept of virtus does change with time. I will get straight to the point showing examples of how the concept changed, given that the topic could be discussed at a significant length which would only end up in digression. Our sources that discuss Roman virtue begin in the Second Century BC, which means we do not fully understand how the concept developed before hand without making assumptions.

Early Roman citizens were predominantly farmers and therefore the concept of virtus to them would have been, according to Ferguson (Moral Values in the Ancient World), "a capacity for hard work, an ability to endure the weather, and courage in facing robbers and wild animals." The example for this is Lucius Quinctius Cincinnatus who during an invasion was found ploughing his fields, was called to lead the defence and then upon his success, returned back to his farm to continue the work.

By the time we get to the period of Scipio Africanus and Cato, Rome was engaging in a significant amount of wars and therefore the concept of virtus became skewed towards success in military matters (vir itself being used to describe fighting men or soldiers). That does not mean, however, that we should solely associated the concept with war during this period. Plautus makes reference to virtus sixty-six times in his plays with his definition being one of courage, however, the courage he relates to is not always martial courage (McDonnell, Roman Manliness: Virtus and the Roman Republic). Likewise, Cato himself refers to the best agricultural land as having natural virtus (On Agriculture. 1.2).

The conclusion of Rome's wars during the period of expansion and the following import of Greek culture seems to have had an effect upon how the concept of virtus was discussed. Cicero describes virtue as being the ability to overcome fear and death (Tusculanae Disputationes. 2.43) and as being a disposition of the soul (Tusculanae Disputationes. 4.34). As you can see, the concept has been expanded to encompass a position in which anyone could have virtus rather than only those of the aristocracy. However, the underlying feature of the concept is still regarding the idea of displaying courage, albeit in a more ethical manner. We still find in writings from the likes of Sallust, and even Caesar, that virtus still had its meaning of martial courage.

Within the principate under Augustus, we are provided with the episode in which he is provided with the golden shield in recongition of his qualities, virtus being one of them which is associated with courage. However, the concept of martial virtus seems to disappear under the Julio-Claudians. Republican coins consistently referenced virtus but under the Julio-Claudians is pretty much is non-existent. Seneca (writing during the period) also promotes the concept of virtus regarding it's philosophical ideas rather than the traditional military concept. It is suggested that the reason for this is that displaying military virtus was no longer a benefit politically as it was a reminent of those who had taken power during the Late Republic.

The concept however returns back to its Republican roots from the Flavians onwards, including Marcus Aurelius. Here it begins to be depicted once more within its traditional form of manliness. There are coins of Marcus Aurelius which depict virtus and the engagement in an activity such as hunting or combat.

 

So, did the idea of virtus change from the period of Scipio Africanus to the period of Marcus Aurelius? Not really. Virtus is a Roman concept that had a significant place in politics which means the idea of what virtus was existed consistently within time. The difficulty is that virtus itself had a variety of definitions even for those of the period, so whilst the concept did not really change from it meaning some form of displaying excellence, it was significantly expanded to include a variety of factors. I hope I have provided enough information for you to get a better understanding, there is a lot more evidence that could be discussed but I have tried to summarise without disgressing from the question.