Of course you can, otherwise smart objects would be totally useless don't you think...
A smart object is basically a shortcut. Example; right click on a layer and notice the option "convert to smart object". Once a layer is converted you can not edit any pixels directly, but you can once you open the smart object.
Here's a quote of Photoshop’s help:
"You can’t perform operations that alter pixel data—such as painting, dodging, burning, or cloning—directly to a Smart Object layer, unless it is first converted into a regular layer, which will be rasterized. To perform operations that alter pixel data, you can:
- edit the contents of a Smart Object
- clone a new layer above the Smart Object layer
- edit duplicates of the Smart Object
- or create a new layer."
His problem however (so it seems) is that he can't open the smart object, if that's the case he has to use your method, but I say again... if everything works well one should at all times be able to edit the smart object.
