Change the MagTag program you want to run at startup.

code.py

# This file should be saved as code.py
# At MagTag startup (or at wakeup time), keep one one of the 4 button pressed.
# The MagTag will switch to the program you choose and remember that decision at each wakeup.
# The trick is to have for each button one CircuitPython program to import.
# You can customise the app_to_start list, here is the current setting:
# no button => magtag_weather
# 1 (D15) => magtag_showtimes
# 2 (D14) => magtag_tree
# 3 (D12) => magtag_spacex
# 4 (D11) => magtag_year_progress_percent 

import alarm
import board
from digitalio import DigitalInOut, Direction, Pull

print("Checking if one of the button is pushed at startup.")

# Four button, but 5 applications to start, if no button is pressed then app[0] will be used.
buttons_pin = [board.D15, board.D14, board.D12, board.D11]
app_to_start = ['magtag_weather', 'magtag_showtimes', 'magtag_tree', 'magtag_spacex', 'magtag_year_progress_percent']

pushed=None

for idx, val in enumerate(buttons_pin):
    btn = DigitalInOut(val)
    btn.direction = Direction.INPUT
    btn.pull = Pull.UP
    if not btn.value:
        pushed = idx + 1            # Shift by one, zero as a special meaning
    btn.deinit()                    # Pin must be release for MagTag library to use it.

if pushed is not None:
    alarm.sleep_memory[0] = pushed
    print("Button pushed:", pushed)
elif alarm.sleep_memory[0] not in range (0,5):
    print("alarm.sleep_memory[0] forced to zero as it had unexpected value: ", alarm.sleep_memory[0])
    alarm.sleep_memory[0] = 0       # Force 0 if the value is not expected.

# Start the application requested

import_me=app_to_start[alarm.sleep_memory[0]]
print("Starting ", import_me)
__import__(import_me)

Improvement:

• a 5th application is possible when no button are pressed, that is the default when powering up
• the applications to import are now into an array of 5 positions