Of course you can, especially as sand is inert. You might want to rinse it first. Then there are several ways to do it without too much mess.
Turn off your filter / powerheads, just in case. Use a length of hose (5/8" works), position one end just over the spot you want to fill, keeping the other end above water. Add sand using a funnel. 2 sets of hands are usefull.
One set of hands method, that I saw on TPT, is to fill a 2 litters soda bottle with sand, close the top with a finger, insert the bottle unto the tank over the spot, use your finger as a gate.
Courtesy * Integrity * Perseverance * Indominable Spirit * and Self Control
Tenets of TKD