[Exim] Local Variables in Filters

I have looked for this several times now in the docs. I am pretty sure
that filters do not support any form of a user defined variable and also
do not support macros.

1) Is this true?

2) Can I add local (scope = filter script) variables to the wish list?
Even if they are just like the $nx vars. Something that can be assigned
a string for substitution latter. (Macros would work also)

Why, because my system filter file is getting unreadable with
repetitions of tests, lookups and expressions. Help!!