Can you replace a Joker with a bonus joker?
I don't think this is possible.
In the rules is the line &quot;Special jokers cannot replace a Regular Joker or any other type of special joker.&quot;. This implies you can not replace the joker directly.
But I think you should be able to rearange sets.

Special Jokers
Special jokers cannot replace a Regular Joker or any other type of special joker.
Reminder: Any set that is laid on the table must consist of at least 3 tiles. In any case (even when you have a Double Joker), you are not allowed to leave sets with two tiles on the table.
In scoring the initial meld, the special joker represents the number, or numbers, it replaces. Note: The Mirror Joker’s value is zero.
Special jokers can be cleared in the same way that the Regular Jokers are cleared, including that they must be played on the same turn and that the player must play at least one tile from his/her rack on that turn.
Double Joker
This special joker fills in two numbers. In a group it represents two of the same number; in a run it represents two consecutive numbers. The Double Joker can only be used inone of these two ways.
For Example:
Run: 2 - Double Joker - 5. The Double Joker represents the numbers 3 and 4.In the initial meld, this tile is worth the value of both numbers it represents(in this example, the value is 7).
Group: Blue 3 –&gt; Red 3 – Double Joker. The Double Joker represents Yellow 3 and Black 3. In the initial meld, this tile is worth the value of both numbers(in this example, the value is 6).
A Double Joker can be replaced with both tiles that it represents in a set or bymanipulating a set to clear it.
The Double Joker tile can be used in any place in a series; as the first, last or middle tile.
The Double Joker cannot be used before the number 2 or after the number 12(only 1 can come before 2 and only 13 can come after 12).