If Denethor hadn't committed suicide

[Inziladun]

Originally Posted by Erendis

Concerning the term "disguise",I think it was not a physical one,because unless he could have his entire face hidden,indeed everything on Aragorn was not only crying"Numenorian blood",but also "Nobble Numenorian blood".I believe a shady and rumor-like story concerning his origins is more likely to be the disguise,more similar to the "undercover" term.Perhaps stories as ,for example,half Numenorian from the North(Dail maybe?),being spread around the soldiers with his consent,if not willingly by him,is a scenario.

Why not a physical disguise? Perhaps he grew a long beard.
Deceiving the Rohirrim would not have been so difficult anyway. If they recognised Thorongil as a Dúnadan, their assumtion would probably have been that he was of Gondor.
When dealing with the Men of Gondor, I think a physical disguise would have been a necessity, for the reasons you cite. If they knew Thorongil was not from Gondor, yet recognised in him Númenórean lineage, wouldn't that have been counter to Aragorn's purpose in going to Gondor in that manner? He wished to see the state of affairs in Rohan and Minas Tirith, and give the rulers in both places some good advice, once he gained their trust. He did not want to stir any controversy.