Parameter driven components and the replace components feature

Hi! 

I'm a new creo convert, so still learning my way round. I've got an assembly, which comprises of essentially a pair of cylinders that extend, and a framework linking them. The cylinder comes in three different length variations, but the width between the cylinders varies. 

At present each product variation is created by parametrically controlling the distance between the cylinders which drives the sections of frame between. However at present to swap between the three cylinders the sub assembly is swapped over via using the 'Replace Selected Components or UDF' function, and this works perfectly at the moment.

However, I want to try and automate the generation of the cover which goes over said frame, and at the moment the width is done parametrically, however the length requires manual intervention. I've already got inside each of the cylinders a parameter for the cover length which in the top level works, but as soon as I change the cylinder this link is broken and it won't find the (same) parameter in the new assembly.

Is there a way to make this work?