What I mean is, if your background and story doesn't agree with what the rules say you should have, then generally speaking, the philosophy of 5e design (as it's discussed in the handbook and the dmg for setting up the world, running the game and characterisation) is to allow the background and story to trump the rules. They recommend DMs and players lean into their personal story more heavily and agree on alterations that suit; my bard, for example, doesn't have full control over her magical capabilities, or a good understanding of them yet; I've got the mechanics in the background, but the in-game reality is that I don't have on-demand access to some of that stuff yet, even though by the written rules I should, and sometimes it happens by accident in stresfull situations.
That has been around for the longest time - it's a base rule. In fact, 3.5 had so many alternate systems to allow people to build a game that allowed them the freedom to play they way they wanted. If you want to make your elf proficient with a battle axe instead of a long sword - you merely needed to explain why.
Altering the Way Things Work
Every rule in the Player’s Handbook was written for a reason. That
doesn’t mean you can’t change some rules for your own game. Perhaps
your players don’t like the way initiative is determined, or
you find that the rules for learning new spells are too limiting.
Rules that you change for your own game are called house rules.
Given the creativity of gamers, almost every campaign will, in
time, develop its own house rules.
The ability to use the mechanics as you wish is paramount to
the way roleplaying games work—providing a framework for you
and the players to create a campaign. Still, changing the way the
game does something shouldn’t be taken lightly. If the Player’s
Handbook presents the rules, then throughout the Dungeon Master’s
Guide you will find explanations for why those rules are the way
they are. Read these explanations carefully, and realize the implications
for making changes.
Consider the following questions when you want to change
a rule.
• Why am I changing this rule?
• Am I clear on how the rule that I’m going to change really
works?
• Have I considered why the rule existed as it did in the first
place?
• How will the change impact other rules or situations?
• Will the change favor one class, race, skill, or feat more than the
others?
• Overall, is this change going to make more players happy or
unhappy? (If the answer is “happy,†make sure the change isn’t
unbalancing. If the answer is “unhappy,†make sure the change
is worth it.)
Often, players want to help redesign rules. This can be okay,
since the game exists for the enjoyment of all its participants,
and creative players can often find ways to fine-tune a rule. Be
receptive to player concerns about game mechanics. At the
same time, however, be wary of players who (whether selfishly
or innocently) want to change the rules for their own benefit.
The D&D game system is flexible, but it’s also meant to be a balanced
set of rules. Players may express a desire to have the rules
always work in their favor, but the reality is that if there were no
challenges for the characters, the game would quickly grow
dull. Resist the temptation to change the rules just to please
your players. Make sure that a change genuinely improves your
campaign for everybody.
However, whereas previous versions were much more open about what fit into different categories, 5e went hard to narrow it down and reduce everyone to stereotypes - that is where there was change. Neutral and evil clerics used to be able to rebuke dead instead of turning them - that is taken away and all clerics act like good clerics, even if they worship an evil deity. The storytelling focus with 5e comes from having FEWER rules and fewer calculations that free up players to focus on telling the story instead of working on character sheets. 3.5e was too complex for some and 4e was just a hack and slash fiasco that few cared for - 5e went simple everywhere to make the game go faster. The result, however, was stereotyping and constraining character builds.
