Dear Simon,
Please note that in ElastoDyn there both tower analysis nodes and stations used to define tower sectional data. Input TwrNodes determines the number of analysis nodes used for the integration of the elastic and inertia forces of the tower. Input NTwInpSt defines the number of stations used to define the tower sectional data in the tower input file. For example, if the tower is uniform, only one section needs be defined, so you may set NTwInpSt to 1. However, increasing TwrNodes always results in a more accurate integration of the elastic and inertia forces, at the expense of slowing down the simulation. Typically, TwrNodes should be chosen in the range of 10-20. ElastoDyn will always interpolate the table of input sectional data (defined by NTwInpSt) to the locations of the analysis nodes (defined by TwrNodes). So, it is not really possible to define true point masses along the tower in ElastoDyn.
Best regards,