absolutely, (the onlihe help in the SOP) if you look at the construct:
[lc<]pred[>rc]:cond=blahblahblah...
the ":cond" part is where you plug in the controlling params....
for instance
premise : A(0)
A(i):i<5=FA(i+1)
A(i)=+60FA(i+1)
would execute the first rule 4 times, and switch to the second one after that.
always remember the L-systems read the rules top to bottom and use the first rule that is valid, so you can have a host of rules that are all A, the L sys will go through them one by one and only apply the first valid one...
and the first 2 variables can have a special meaning for the length and thickness say so A(k,l,m) the variables (k) and (l) are multipliers for the length and thickness (uh...check the docs for this maybe the PDF, haven't used L-sys in a while...)
don't forget to use the "b,c,d" user vars in the "Values" tab, they allow you to control features for the whole system . For instance, in the preceding example replace i<5 by i<c set the generations to something higher than 5 and play with the c slider, the system should change immediately....it's a way to affect the whole look of a system from one variable...
Most of the stuff here is a direct derivation from thew book, I just had to adapt the syntax a little bit, but the book is full of insights like these...
hope it made sense...now go forth and go nuts!
Cheers!!