Fallout 76 doesn't really many new things to the universe, except for multiplayer and the way character progression works. The latter will be decided by the classic S.P.E.C.I.A.L. as well as perk cards, one customisable, one not so much.
Bethesda have revealed that perk cards will be interchangeable at any given moment back when the perk cards were shown for the first time. This offered a wide variety of builds for players to utilise while navigating and looting Apalacchia, and presented a welcome twist on the rather lacklustre perk system in Fallout 76.
The number of specific cards or the maximum card level a player can use will be restricted by SPECIAL though. For example, if a player has 10 strength, they will only be able to equip strength-related cards whose level will add up to the maximum of 10. Therefore, one can equip two level four cards with a level two card, 10 level one cards or any other combination where the total card level doesn't exceed the related SPECIAL attribute's level.
Mix and match will sure prove to be fun for Fallout 76 players, but as the title suggested, it will not be limitless. One fan has asked if they would be able to re-spec SPECIAL, as they could potentially reach level 50 and be unhappy with their build. Pete Hines with a simple "you cannot respec your SPECIALs".
This answer drove many fans into despair as they hoped they would have options, especially when the first character they create will most likely prove to be the worst one as they don't have a grip on perks and optimal builds yet.
All of these concerns were left unanswered at the time of writing, and it remains to be seen if Bethesda will eventually add a re-spec tool or start selling it for Atoms. While the latter would not be optimal, it would still be better than having no options at all. On top of everything, such a feature could function as an effective currency sink, should it be implemented.