Are magic items usable while crafting an upgrade?

[Christopk-K]

I want to upgrade a headband of Cha+2 To Cha+4 a sword from +1 to +2 a ring of protection from +3 to +4 that sort of upgrading trough crafting.

We play a campaign where we spend a lot of time travelling but have regular encounters along the way.

So my question is, can I still use these items in their original form, e. g. sword +1 while over the course of several weeks adding the enchantment to make this into a sword +2?

[Fuzzy-Wuzzy]

This is not explicitly addressed by RAW, but IMO the absence of rules saying it stops working suffices to show that it keeps working.

[Kayerloth]

No clear cut answer to that one that I know of. Expect a lot of variation between DMs and even differing campaigns with the same DM.

[blahpers]

Not covered. Expect table variation.