F23A4 engines were ULEV (Ultra Low Emission Vehicle). F23A1 were generally non-ULEV.

I believe both F23A1 and F23A4 were SOHC VTEC engines. The ULEV engine was similar to the non-ULEV, the main differences were the exhaust manifold, a more restrictive intake manifold and cylinder head, and the PCM/ECM.

You should be able to swap the exhaust manifold and intake manifold from your previous engine on to the replacement engine and use your current PCM. If you use your current PCM, there is no need to reprogram it for to the Immobilizer System (if you replaced the PCM, reprogramming for the Immobilizer will be necessary unless it was bypassed/disabled.)

There were some differences in models years between 98 and 00.
Differences in model years (not because of ULEV vs. Non-ULEV)
Wiring for temperature gauge slightly different.
1998-99 Accord: Engine coolant temperature signal is from coolant temperature gauge sending unit. 98-99 Accord had Yel/Grn wire from coolant temperature gauge sending unit to Gauge Assembly Connector pin C2.
2000-02 Accord: Engine coolant temperature signal is from PCM. 00-02 Accord had Yel/Grn wire for Engine coolant temperature signal from PCM Connector pin C24 to Gauge Assembly Connector pin C2.

Difference between ULEV vs. Non-ULEV (98-02)
ULEV had Air/Fuel Ratio sensor. If you used your current exhaust manifold and PCM, you can just use the regular O2 sensors.