Answer

Based on the rulebook context, specifically page 13, the following applies:

• Yellow-background cards are "generic activities," and "a player chooses separately for each of these cards whether to count it as Tokyo or Kyoto."
• This choice is made "for each of these cards," and the context does not specify a timing restriction relative to Train token placement.
• Train tokens must be placed "each time a player will be traveling from Tokyo to Kyoto (or vice versa)" between Activity cards in their itinerary.

Manipulation for Fewer Train Tokens

• Since the player chooses the city for each yellow-background card, and the rulebook does not specify that this choice must be made before planning or before Train token placement, it is implied that the player can assign the cities at the time of Train token placement.
• Therefore, the player can assign consecutive yellow-background cards to the same city to avoid placing a Train token between them.
• This allows the player to minimize the number of Train tokens by strategically assigning cities to yellow-background cards.

Supporting Citations

• "Some cards have a yellow background and do not list a city. These are generic activities, and a player chooses separately for each of these cards whether to count it as Tokyo or Kyoto." (page 13)
• "Each time a player will be traveling from Tokyo to Kyoto (or vice versa), they must place one of the following Train tokens between the Activity cards in their itinerary..." (page 13)

Summary

The player assigns the city for each yellow-background card at the time of Train token placement, and may do so in a way that minimizes the number of Train tokens required by assigning consecutive yellow-background cards to the same city.

Source: page 13

Source: Base Rules (pp. 13, 16, 2, 3, 7)