Will my smartobjects be effected if I change the ps-file 72 dpi to 300dpi?

All smart are not created the same way how smart object layer behave/works depends on the smart object and what you are doing with the smart object layer.   Some Smart Object are Photoshop objects some smart objects are not Photoshop objects. If you double click one at smart object Layer's Content Thumbnail in the Layers Palette to open it and work on it. Photoshop will create or has create a temp work file in temp space  and it will be opened for you to work on.  If it is a Photoshop object it will open in  Photoshop.  If it is a RAW object it will open in ACR. If it is a Vector object it will open in your vector application  Illustrator.  Smart Object have pixels generated for them that photoshop will use.  These pixels are harden and can not be changed by Photoshop tools. There is a transform for smart  object used to create the smart objects Layer's pixels.  When you transform a smart object layer what you are doing is editing the existing object transform to scale the object to a different size. transform interpolate or copies object pixels to generate the layers pixels.  However, there are exceptions Vector Object AI objects  are processed with vector graphics.  Photoshop does  not have support for Vector Files.  Photoshop has an imported that can via vector graphics create a pixel layer the size the user set.  Basically Photoshop Imports the Vector Object's file the appreciate size to replaces the prior old harden image pixels that get transform 100% to the layers pixel. There are no vector in photoshop for vector objects.  The vectors are in the vector object's file the ai file. You need to get you AI asset into Photoshop as smart object later.  I do not install AI there may be a way to paste in AI file as smart object,.  When I use paste I either paste a clipboard pixels image or clipboard text. I would think Adobe could have  a copy and past object between their applications. I can Placet in AI file as Smat Objects.