Interesting thread!
There were at least one certain example of an attempt to introduce Germanization (via Teutonic Order). After the "formal" baptism, Vytautas the Great eventually centralized the country by using similar to TO model. Looking from cultural point of view we see that castles, notably Trakai, Vilnius (XV) also were built by TO in the same manner. Problem that in ± 1427 Lithuanian slaughtered almost all christians, particularly in Western Lithuania (Samogitia), Northern part of LT. Southern part of present-day Lithuanians territory remained pagan (Bishops from Czech wrote about it). The main issue was connected to the fact that pre-christian GDL (Lithuania propria) country and society in general was based on pagan culture and it turns out that society consisted of "free folks" - an opposite to TO/Germanization/. You can not use similar "nobility property" laws on the society which was based on a free people. Even Vytautas the Great knew that and for this reason he deported all local people from Trakai
Slavic parts of GDL were Christians so there was no reasonable background to adapt a
germanization because it subsequently might end up in revolts (back than Moscow was starting to breath). Except economical model of "germanization" which was by the way more advanced. And the economcal model, which seemingly was a "copy -paste" from Teutons, was relatively adapted for a short period of time. It also contributed to the final centralization of really large country.
Invading. T.O have never won any decisive victory against Lithuanians. But if Livonian Order was not so dangerous for Lithuanians, particularly after all major victories against them, Teutons were a serious threat.
What they did was
a raiding (raisse?). It affected some parts of LT that indigenous people was forced to emigrate from those places and in turn certain lands later became a "wild land" (dykra).
Some mind food:
1. Pretty intense emigration from other Baltic tribes, notably yotvingians, bartians (prussians), semigalians, curonians etc. Therefore GDL always had an experienced human resource, particularly from XIII-XIV centuries. There aren't, however, clear evidence that Slavic people would fight with Lithuanian especially against T.U. As far as I know, latter event was mentioned only once. I assume that a notion of "christian vs christian= not good" was in effect.
2. Militarization. It is a myth that pagans Lithuanians had no adequate military equipment. Keeping an eye on burial grounds since X cent. you wont find more militarized tribe than Lithuanians in whole Europe.
Probably the best known achievement is so-called "lithuanian" or "prussian" shield. Even in women grave you could find a knife or an axe.
In fact, it is understandable - in Christian Europe (XIII-XV) social stratification (farmers, nobles ets) was more developed and who was a knight and what kind of duties he had we all know. It was opposite in GDL.
3. Paganism. Lithuanian paganism was more pro-military ant it well served on so called "war-democrasy" and establishment of one local duke/political center (Myth of Sventaragis and Vilnius). Let's pay an attention that the baltic society was individualistic society.
4. Behaviour. Stubbornness still is something we appreciate most. Fanatical behaviour - furiosity - was a best thing that saved Lithuanian asses. Even in XX century, during Anti-Soviet Resistance, a fanatical furiosity became a true horror for soviets KGB soldiers.
5. Society. Differently than in "Christian world" (including Slavic territories of GDL), Lithuanian had not such perception "only noble knight must fights". Therefore you can be a farmer, a peasant "in the peace time" but when it is a war time (it lasted ± 200 years) - you a fighter. So there was no human limits to raise an army.
6. Forest, swamps - natural barriers. Usually T.O lost majority of small wars when they were forced to fight in the forest or on the swampy land.
7. Growing centralization.