@JeremyECrawford Was it ever officially said whether a Bard can retrain spells gained through Magical Secrets, or not?
— wyndll (@wyndll) October 24, 2015
A spell learned via Magical Secrets counts as a bard spell, so it can be replaced upon gaining a level later. #DnD https://t.co/d17GnGHaiT
— Jeremy Crawford (@JeremyECrawford) October 24, 2015
@JeremyECrawford @wyndll can it be replaced with a new magical secrets spell or must ot be from bard spell list?
— Ryan Hagan (@SalmonSquire) October 24, 2015
If a bard replaces a bard spell upon leveling up, the new spell must also be a bard spell. #DnD https://t.co/lrM72VeK2S
— Jeremy Crawford (@JeremyECrawford) October 24, 2015
That ruling actually sucks. So the next question is when a bard qualifies for magic secrets at 10, 14 and 18 (and 6 for lore bards) do you have to select the spell then or can you opt to select the spell when you reach higher levels. For example a lore bard waiting until 7th level to pick up a level 4 non-traditional spell.
That was supposed to be non-bard spell
The rules are intentionally designed to prevent players abusing it in that manner to circumvent the spell level restrictions. You pick when you get your Magical Secrets (nothing allows you to delay that choice), and you can only pick spells of a level you can cast at the time the selection is made. A Lore Bard’s 6th level Magical Secrets are limited to at most 3rd level spells.
It doesn’t actually suck as a rule, but rather makes perfect sense relative to the feature allowing bards to access essentially any spell of the appropriate level outside their list (a very powerful feature), but not before — or even at the same time — as that given spell will be accessible to “x” class as appropriate to that class’s spell list. That is, using a Lore Bard for example purposes: at 6th level, the LB can choose 2 out-of-class spells up to 3rd level (that is, a level after another class would have appropriate access at 5th caster level); at 10th level, the bard has access to 2 up to 5th level OoC spells (upwards of 3 levels, for example, after in-class casters would have access to their 4th level spells); etc…
It actually makes perfect sense when you stop to think about it for a moment.