Filtering problem

I have inherited some XML files that I need to filter.
Because i have inherited the files I did not design the way the elements
were tagged.
But I have to write the xsl to do the filtering - and I am only just
dipping my toe into xsl.

I want to output XML - that I will feed into FrameMaker for typesetting.

I want to filter on a number of dimensions.

For various hysterical reasons the various elements have been taged with
attributes of the form

<element dim1_a="yes">
or
<element dim1_a="yes" dim1_b="yes">

I want to create a filter that will include all elements where either:

there are no attributes starting dim1
or
dim1_a="yes"

And I need to do this for several dim1 dim2 etc.

If needs be I can run a number of xsl transforms one for each dimension.

I have some other attributes = e.g. role that I need to keep.

Is this possible, or do I need to completely change the way these files
are tagged.

If so can I easily do that with xsl - or do I need to do it by hand.

Thanks

Marcus