grammar - Is it correct to write a noun once while listing two related (verbs) activities?

For instance, in the sentence:

Without adding new items and modifying existing items.

Would it be correct to completely remove the first reference to the noun items? as in:

Without adding new and modifying existing items.

It sounds wrong. Is the only correct alternative replacing the explicit noun with an implicit reference as in:

Without adding new items and modifying existing ones.

Is there a more elegant way to avoid writing the explicit noun twice in this sentence?

I read this: Mixing adjective and noun enumerations but did not find it very useful.

Answer

I think that the addition of a comma would help

Without adding new, or modifying existing items.

The comma introduces a slight pause that suggests the missing, but implied items.

You will note that I substituted or for and. While the context is not provided, your example seems to suggest neither of the two conditions will occur. If you were to use and, it might be ambiguous and could be taken to mean neither would happen or that the concurrence of both would not happen.