SVN ignore file in parent branches

I want certain files/folders to be version controlled at a certain "level" branches and below (meaning branches that are branched from that branch) but want to ignore them upward. Can I achieve this?

Rephrasing: I have multiple projects which are fairly similar, but differ in certain files (1-2 files). I would like to have a main branch for all the common stuff and have branches to keep the special behavior. This way I could easily merge fixes between the projects via a common ancestor but also manage the special aspects of them (and versioning them). Is this achievable?

Example:

Root (Not a full project):
- 1
- 2
Project A (parent: Root):
- 1
- 2
- q
Project B (parent: Root):
- 1
- 2
- w

Solution

Eventually I settled on the 'external approach':

All common stuff is in master, all projects branch from master and there is an external folder added which has a relative path in the repo. The project specifics are put in this folder which is another repo on itself, only available in their respective project repo.

master
project1
|-specific
  |-spec
|-trunk (parent is master)
  |-spec: external ../specific/spec
project2
|-specific
  |-spec
|-trunk (parent is master)
  |-spec: external ../specific/spec

So all merges between the common parts are possible and no project specific components end up in other projects. Side effect: the master cannot be used on it's own.