Customizing vendor-supplied interfaces

[Jerry Kuntz]

We're implementing a new web-based PAC product from our library automation vendor that offers a great deal of flexibility for customization. A limited amount of that customization can be done via administration software the vendor has supplied. A great deal more can be done by making changes to the default XSL templates supplied with the product.
Some sites using the same PAC product have done extensive customization of the XSL, adding many features we're interested in, too. The danger in copying these independent customizations is that they may be wiped out with the next upgrade from the vendor. For example, one site has reported it took them 40 work hours to re-customize the product when it was upgraded from 2.0 to 2.01.
We don't know whether to invest our local resources into customization [realizing that work will need to be strictly documented and re-created, and adding to the cost of implementation] or whether to put wait and put pressure on the vendor to incorporate these features into their standard admin software. 
I'm sure this is a quandry that has been around for years--decades--but I'm just wondering if any library has developed general guidelines or policies; or are these taken case-by-case?

--
Jerry Kuntz
Electronic Resources Consultant
Ramapo Catskill Library System
jkuntz at rcls.org

--