There are so many layers to untangle here I am genuinely not sure where to start. Let's perhaps begin with the issue of access to charts:

an Italian peasant, only obtained access to Portuguese navigational maps through his wife, the noblewoman

The thing is that very simply it wasn't the only way he could obtain access to Portuguese maps. In fact, we aren't sure if it was even a way he got access (but more on that later). Maps of that time just weren't in any way forbidden to commoners. Almost the opposite, they were designed for commoners.

To give a bit of context: while some of the maps - called the portolan charts - were highly decorative world map pieces that rich / nobility could purchase and showcase, the majority were a instrument to be used by the medieval (mostly Mediterrenean) ship navigators. And 15th century ship navigator was an occupation reserved purely for commoners as nobility wouldn't demean themselves with such a "job". Even in those instances when a noble would be given a "captaincy" of a ship - a title reserved for nobles - the role would include only overall command and high level decision making, the actual day to day operation of the ship would be handled by the "master" while the navigating would be done by the "pilot". Pilots would plot courses using compasses on these charts and they were the intended customers of the chart makers and sellers, who in turn were also more often then not commoners. And in example of Iberia, often Jews - an even more marginalized group then commoners.

To add, Columbus' brother Bartholomew (also Christopher himself) was in the 1470s noted to be a map maker in Lisbon. The usual way events are reconstructed say that when Columbus reached Lisbon in 1473 he merely joined his brother who was already there working there as a cartographer. It was only much after that Columbus married his wife in 1479. But mind you there is no evidence actually backing the dates, or the order of events so it is possible it was different. In each case I believe Bartholomew Columbus' example shows how a foreign "commoner" could with no problems become a map maker and chart producer in Lisbon (if he had the skills), meaning him and his brother would have easy access to Portuguese navigational maps.

If he already couldn’t get access to those maps

To expand on this, I believe this idea that Columbus, or anybody for that matter - couldn't get access to Portuguese maps probably comes from the often brought up Portuguese policy of Secrecy - a factual thing but one which has in both Portuguese historiography and especially so in popular culture been bloated up to mythical proportions across time and its scope. The actual decree proclaiming the Policy was indeed a real thing. It was from 1504 by King Manuel (with some indications Joao I in 1480s toyed with a similar idea) and proclaimed that no maps and information past Cape of Good Hope is to be shared with foreigners. Even in Manuel time the decree was unenforceable, and accomplished little, but the main thing is that it really wasn't a thing in Columbus time.

Look at this [map of African coast](https://commons.wikimedia.org/wiki/Category:Maps_by_Grazioso_Benincasa#/media/File:Portolano_(Egerton_MS_2855,_f.7r).jpeg) from Italian map maker Benincasa made in 1473 and pretty much shows entirety of Portuguese knowledge of the coast at the time. Or this [map](https://commons.wikimedia.org/wiki/Category:Cornaro_Atlas#/media/File:General_chart_of_the_coasts_of_Europe,_the_Black_Sea,_the_Mediterranean,_and_the_western_coast_of_Africa_south_to_Cape_Negro.-Cornaro_Atlas(Egerton_MS_73,_f.36r).jpeg) from Venetian made Coronaro atlas dated to 1489. It shows everything discovered by Portuguese (bar the latest discoveries by Dias) with great accuracy. Their existence in Italy shows just how readily available Portuguese navigational maps were.

only obtained access to Portuguese navigational maps through his wife, the noblewoman Felipa Moniz

Out of curiosity I've searched for the origins of the claim, and have found something similar was said by Ferdinand Columbus in his biography of his father, and repeated more cautiously by Las Casas. In the claim, Columbus' wife was of Perestrello family, and Columbus then lived with his mother in law for some time, who in turn have him her late husbands charts and navigational instruments. Now, first thing I want to point out is that some modern historians actually call into question the accuracy of those words (like Miles H. Davidson in his Columbus Then and Now: A Life Reexamined or even super old Christopher Columbus: His Life and His Work by Charles Kendall Adams) and point out that the connection to Perestrello is very weak and not corroborated by anything other then these mentions, and also that the events in question happened before either of the two (Ferdinand and Las Casas) were even born and were told to them by Columbus first son Diego, who also couldn't actually be a real witness as he was at best just a baby/young child (or perhaps not even born) when this transpired.

For us it's not really important to see if that happened or not, but I just want to say that even if this unreliable accounts are taken at completely face value, they do not in any way imply that without these charts Columbus would have no other access to maps / navigational knowledge - especially due to him being a commoner - but more so that this was valuable and appreciated gift as Columbus was already very interested in all things navigation, and at the same time charts and instruments were expensive and not the easiest to get to new ones (as they were handmade and difficult to copy)

then why was he allowed to marry a noble?

We have so little information on who and why Columbus married (as shown above) it really is impossible to even guess, let alone say. I would just say that commoner marriages into nobility (especially lesser and poorer noblity) was much less of an issue then it is implied by your question. It happened, and happened a lot, and I am not sure if there was anything that would "not allow" it, or prevent it if people in question and their families wanted to.