From Nookipedia, the Animal Crossing wiki
For the first 7 days in town, Cyrus will be asleep at his desk, unavailable. According to Reese, Cyrus worked on a project all night and is "extremely tired". After the player has sold 100,000 Bells worth of items, along with having acquired 100 pieces of furniture and 50 pieces of clothing in their catalog, Cyrus's customization services will be available.
When certain furniture is brought to Cyrus, he may offer to paint it and give a list of shades it can be painted. Usually this is one shade lighter, one shade darker and one different shade that can be related to the other colors. Furniture that has been painted will show up as a red leaf instead of a green leaf. The prices vary, but are usually priced around 200 Bells.
When certain furniture is brought to Cyrus, he may offer to change the pattern on it, or sometimes he can paint it and change the pattern. The patterns on the furniture can be cushions on sofas or chairs, bed-sheets on beds, etc. He will ask the player if they would like to use a pattern from their patterns, a pattern from clothing, or just to change the color of the pattern already used on the furniture. If the player chose to use a design from their patterns, he will warn the player that if the pattern used for the pattern in the furniture is changed, so will the pattern used in the furniture. Furniture that has a custom design will show up as a yellow leaf in the pockets instead of a green leaf. The prices vary, but are usually priced around 200 Bells for just changing the pattern or changing the color of the pattern and 500 Bells for painting and changing the pattern/color.
Making furniture from gems
See gem for more on this.
As long as the player can supply Cyrus with a complete skeleton, Cyrus can shrink down all the bones to make a 1 by 1 miniature version of the skeleton. The cost varies between fossils, but is usually around 1,500 Bells.
If the player gives Cyrus three gold ores and 10,000 Bells, he will make a random piece of Golden Series furniture for them. Gold ores are rare and found by smashing "fake" rocks (one fake rock appears each day), and there is also a chance of finding ores by hitting the Money Rock with a Silver Shovel.
If an item such as the carriage from Happy Home Designer is given, Cyrus will comment on the size and wonder how he will fit it onto the table, he will say it is his problem and not the player's to worry about the size. He will still refurbish the item, but will place a reserved sign while doing so. Once completed, the item will be inside a box and can be collected as usual. Completion of the item regardless will still take 30 minutes.
Happy Home Designer amiibo card
Cyrus appears along with Reese in a trophy.
Names in other languages