Learn Dutch: De expert zal dit oude artefact straks taxeren. - The expert will appraise this old artifact later.

Adjectives in front of neuter nouns only drop the -e ending if the noun is indefinite (like when preceded by een or nothing at all). Here, the noun is preceded by the specific demonstrative determiner dit (this). Because dit makes it specific, oude keeps the standard -e ending.

If we applied this lesson's categorical demonstrative to say 'such an old artifact', how would the grammar change?

You would replace dit with een dergelijk to make the phrase een dergelijk oud artefact. Because een dergelijk acts as an indefinite determiner before the neuter noun artefact, the adjective drops the -e and becomes oud.

Why does the time word straks come after the object dit oude artefact instead of before it?

In Dutch, time adverbs like straks usually come after a specific direct object. Because the demonstrative dit makes the artifact a very specific object, it gets placed before straks. If the object were non-specific (like oude artefacten in general), straks would come before it.

What is the exact nuance of taxeren here compared to other words for 'to estimate' or 'to value'?