Does getting one of those 'lite' racquets and adding lots of lead tape and silicone etc make it into a good racquet?
For example, Wilson have several versions of the same racquet in Lite, Team, and Heavy versions.
If I were to buy the Lite version would I be able to customize it so that it plays like the Heavy version but in the way that I want?
Yeah, this is essentially what the pros do with pro stock racquets, which come lighter than stock to make room for customized weighting.
Now, can you make the Lite version of a particular line play exactly the same as the Tour (or whatever they call the heavy version) model? I think that depends on exactly which brand and racquet line you're looking at. Quite a lot can be done using the TW University Reverse Engineering Tool to figure out exactly where to add mass to the Lite version to match the heavy one, but there is always a question about whether the Lite and Heavy versions have the same layup.
Are the layups (amount and orientation of graphite sheets put in the mold) identical except for non-structural weights added to the heavy version? Or does the heavy version have additional graphite layers or something else that fundamentally changes the playing characteristics in a way that adding lead tape or whatever after the fact cannot match? Again, it probably varies by racquet line.
For example, playtest reports from players on this forum suggest that the layup of the Lite version of the Yonex Ai98 is probably identical to the heavy version. The Lite version is simply missing a bunch of mass in the handle (a chunk of lead sandwiched in the hairpin during manufacture) and a couple grams at 11&1.
On the other hand, the RF97 Autograph is significantly stiffer than its little brother, the PS97 (approx. 70 vs. 67), which tells us right away that the layup of the heavier Autograph version probably has more graphite (or a stiffer grade of graphite) in the layup. So you might be able to match the specs exactly but the two models will still feel and play differently.
Now, are those differences of critical importance? Totally depends on the player. Some may prefer the stiffer feel of the stock RF97 while others would like the more flexible PS97 weighted up to match the RF7.
In any case, adding lots of mass to a lightweight frame is by no means verboten, although it can be frustrating if you don't have a clear idea of what you're trying to accomplish (target specs) or how to hit that target with customization techniques.