I am hoping that in some future release of Renoise that the sample highlighting will be more advanced–more like Audacity, Soundforge, etc. What I mean by this is–if I’ve highlighted part of a sample with the mouse, and I didn’t QUITE get all the part of the sample I wanted to highlight, I can go to the right edge or left edge of what I have highlighted and drag it over more in one direction or the rother instead of having to start over again completely on highlighting the part of the sample. When the mouse hovers over the edge of the highlight, it should change the mouse pointer to reflect being able to drag it further one way or the other.
The “begin & end” selection works like you’ve requested, unless I’ve misunderstood you somehow.
I usually use shortcuts such as zoom in/out for precise “begin & end” cuts.
Also, if you “begin” a selection and “end” it at a section you don’t like, you can move to a different section and “end” it there. Not only does it remember where you began the selection, but it works forward and backwards as long as you don’t click a new “begin” section because it’ll override the previous “begin” selection. I hope that makes sense.
I think the key answer here is to use the right mousebutton to adjust the sample end or start once the sample range has been roughly selected with the ususal left mousebutton.
Thanks. Very. Much. 
It would never have occurred to me to use the right button for that… this has been a frustration for me since 2004.
I guess now I should modify my suggestion:
I think the mouse pointer should change when the mouse reaches the beginning or end of the selection–just SOMETHING to suggest that there’s such an option there.
Again, thanks very much