If it is just one variable (length) you are modifying use the variable table. If it is more than a few, go with an excel sheet.
I have used an excel table, and linked values (about 25 for a part) to the variable table in solid edge.
Then, using revision manager, I create copies of that part, which can be modified using the assigned cell in excel for the length variable.
Do this by opening the part file, and then opening the variable table under the tools tab.
Right click on the cell in excel, and select copy.
Then, right click on the "link" cell in the variable table, and select paste link.
You should then see a file path pasted into the variable table.
From this point on, that variable will be controlled by the excel sheet.
-av8errr
Solid Edge ST3 MP5
xw4600
3GB RAM
Core2Quad CPU 3.00GHz
NVIDIA Quadro FX4800