The reiteration of the 'Sector Perform' rating and maintenance of the $90 price target by RBC Capital suggests a neutral outlook on Altair Engineering's stock in the short term. This indicates that the analyst believes the stock is fairly valued at its current level, neither significantly undervalued nor overvalued. Therefore, the impact on the stock price is likely to be neutral in the short term, as the market has likely already priced in the analyst's expectations.