No

It actually wouldn’t make much of a difference at all. By level 9 either getting advantage/huge bonuses on sneak attempts or disguising yourself as another person aren’t terribly hard to pull off if you have spellcaster friends or access to magic items (Invisibility and Pass Without Trace just to name a few, let alone that your sneaky assassin probably has Expertise in Stealth anyway). Neither of these features are particularly strong to begin with, and swapping one for the other is neither going to make or break any particular build.

At any rate, Assassinate is going to remain hard to pull off reliably not necessarily because ambushing a target is hard (although depending on the exact circumstance it often will be), but rather because it’s entirely reliant on the Assassin rolling a higher initiative than their intended target, which neither feature helps with.

If it makes your player happy, I don’t see any issue with letting them have this.

No, this change wouldn't be unbalanced

It actually wouldn’t make much of a difference at all. By level 9 either getting advantage/huge bonuses on sneak attempts or disguising yourself as another person aren’t terribly hard to pull off if you have spellcaster friends or access to magic items (Invisibility and Pass Without Trace just to name a few, let alone that your sneaky assassin probably has Expertise in Stealth anyway). Neither of these features are particularly strong to begin with, and swapping one for the other is neither going to make or break any particular build.

At any rate, Assassinate is going to remain hard to pull off reliably not necessarily because ambushing a target is hard (although depending on the exact circumstance it often will be), but rather because it’s entirely reliant on the Assassin rolling a higher initiative than their intended target, which neither feature helps with.

If it makes your player happy, I don’t see any issue with letting them have this.

No

It actually wouldn’t make much of a difference at all. By level 9 either getting advantage/huge bonuses on sneak attempts or disguising yourself as another person aren’t terribly hard to pull off if you have spellcaster friends or access to magic items (Invisibility and Pass Without Trace just to name a few, let alone that your sneaky assassin probably has Expertise in Stealth anyway). Neither of these features are particularly strong to begin with, and swapping one for the other is neither going to make or break any particular build.

At any rate, Assassinate is going to remain hard to pull of reliably not necessarily because ambushing a target is hard (although depending on the exact circumstance it often will be), but rather because it’s entirely reliant on the Assassin rolling a higher initiative than their intended target, which neither feature helps with.

No

It actually wouldn’t make much of a difference at all. By level 9 either getting advantage/huge bonuses on sneak attempts or disguising yourself as another person aren’t terribly hard to pull off if you have spellcaster friends or access to magic items (Invisibility and Pass Without Trace just to name a few, let alone that your sneaky assassin probably has Expertise in Stealth anyway). Neither of these features are particularly strong to begin with, and swapping one for the other is neither going to make or break any particular build.

At any rate, Assassinate is going to remain hard to pull off reliably not necessarily because ambushing a target is hard (although depending on the exact circumstance it often will be), but rather because it’s entirely reliant on the Assassin rolling a higher initiative than their intended target, which neither feature helps with.

If it makes your player happy, I don’t see any issue with letting them have this.