So after I use “All elements in Active view” I run some filter and then I want from the overriden Elements to select a specific one with “Select Model Element”. But apparently the if statement is not suitable for that (the code does not seem to run properly thereafter). Moreover, in DynPlayer, the Select model element is mandatory to begin the script and I do not want that.
This is fundamentally incorrect for how a if node works.
The “if” node requires a Boolean input into the “Test” input(true or false). You input what you want to happen if the input is true into true slot, then you input what you want to happen in the false slot.
Therefore you need to figure out how to add a true or false into test slot to make it work.
You can use something like that:
From what I understand of your request, you probably need to use datashapes package. It is not possible to manually select from a filtered list of elements with dynamo.
Use the datashapes package UI+ to create a user interface to allow to search through the items found in the filtered list
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Add in a node to hide the elements and end the transaction and you’ll be well on your way. 
Did you try what @danielU3R39 suggested? To me that seems like a plausable solution.
Create a list with overriden elements, and use that as a data|shapes input list. Creates a popup screen from which you could select a or several value(s).