You should minimize the use of ext at all cost. If you need
to change some implementation: Most likely you just found the wrong
solution for the underlying problem. In the few cases where you
actually need to change the implementation (through ext): Go ahead,
but minimize the size of the ext. Then add whatever you need on top,
in regular modules.
Your future self will thank you when they'll have to upgrade that
code to the next version.
And if you don't have to upgrade the code yourself: Assume those who
will need to do it know where you live.
Seriously: Ext can easily introduce a maintenance burden, which
should be minimized at all cost. It's Liferay's business to change
their implementation. If you interfere with that, you'll have to do
the three-way-merges on every individual upgrade - worst case even on
minor upgrades or, in case of DXP, from Fixpack to Fixpack. Don't go
there if you don't absolutely have to.
