rts package for downloading MODIS data. But is it possible to specify cloud cover and view angle before downloading? e.g. if I want to download MODIS data for cloud cover less than 10% and view angle of 10 degrees.
Unfortunately the answer is no. The way you asked the question makes me think you are comparing MODIS products with Landsat, which allows you to specify cloud coverage as a threshold during data query. This is not the case with MODIS. However, you can deal with it yourself simply by using the associated cloud mask. In your specific case, the MOD11A1 product does provide daytime and nighttime clear-sky coverage, which can help you achieve that.
Also, the MOD11A1 product includes two bands recording the zenith angle of the observation at each pixel, which I believe can provide you with the information regarding the view angle.
It is possible if done via LandViewer. Once you locate an area of your interest you will have an option to filter the images based on cloudiness level on the top right and download them with ease via download button on the right. An example of such imagery can be seen here or you can view It on the platform directly here.