Replacing LED with Flashing LED in a circuit
Flashing Leds operate in one of two ways inside. The first, I was told by my electronics class teacher a decade ago. The Led has a thermal wire or metal inside, that when heated up, flexes &amp; breaks the connection. Once the connection is broken, the wire cools down, and flexes back, making the connection again. This makes the led flash. Since the Led Junction itself produces heat (and light) when power is turned on, only the thermal wire is needed. Works like a miniature version of a car turn signal flasher. These might not require a resistor, I am not certain.

The second version uses an embedded microcontroller/ic to do the flashing. Similar to the self flashing rgb leds.

In either case, these both provide one other function. They break the connection between the two leads of the led. Any regular led in series with them will flash at the same rate, because power is physically cut off. In this case, since the led is tied to ground, once the led makes the connection, the base of the q1 and q2 transistors are affected, disabling them.

As for replacing them, you could not do it easily, without a microcontroller atleast. The Flashing Led is a critical part of a FLED Solar Engine. Here is a wiki with a more detail explanation on how FLED Solar Engine's work.